10 files changed, 1330 insertions, 637 deletions
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index a6974e9b8ebf..1e2cb846b3c9 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -1,6 +1,8 @@
-/*P:400 This contains run_guest() which actually calls into the Host<->Guest
+/*P:400
+ * This contains run_guest() which actually calls into the Host<->Guest
 * Switcher and analyzes the return, such as determining if the Guest wants the
- * Host to do something.  This file also contains useful helper routines. :*/
+ * Host to do something.  This file also contains useful helper routines.
+:*/
 #include <linux/module.h>
 #include <linux/stringify.h>
 #include <linux/stddef.h>
@@ -24,7 +26,8 @@ static struct page **switcher_page;
 /* This One Big lock protects all inter-guest data structures. */
 DEFINE_MUTEX(lguest_lock);
-/*H:010 We need to set up the Switcher at a high virtual address.  Remember the
+/*H:010
+ * We need to set up the Switcher at a high virtual address.  Remember the
 * Switcher is a few hundred bytes of assembler code which actually changes the
 * CPU to run the Guest, and then changes back to the Host when a trap or
 * interrupt happens.
@@ -33,7 +36,8 @@ DEFINE_MUTEX(lguest_lock);
 * Host since it will be running as the switchover occurs.
 *
 * Trying to map memory at a particular address is an unusual thing to do, so
- * it's not a simple one-liner. */
+ * it's not a simple one-liner.
+ */
 static __init int map_switcher(void)
 {
        int i, err;
@@ -47,8 +51,10 @@ static __init int map_switcher(void)
         * easy.
         */
-        /* We allocate an array of struct page pointers.  map_vm_area() wants
+        /*
-         * this, rather than just an array of pages. */
+         * We allocate an array of struct page pointers.  map_vm_area() wants
+         * this, rather than just an array of pages.
+         */
        switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
                                GFP_KERNEL);
        if (!switcher_page) {
@@ -56,8 +62,10 @@ static __init int map_switcher(void)
                goto out;
        }
-        /* Now we actually allocate the pages.  The Guest will see these pages,
+        /*
-         * so we make sure they're zeroed. */
+         * Now we actually allocate the pages.  The Guest will see these pages,
+         * so we make sure they're zeroed.
+         */
        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
                unsigned long addr = get_zeroed_page(GFP_KERNEL);
                if (!addr) {
@@ -67,19 +75,23 @@ static __init int map_switcher(void)
                switcher_page[i] = virt_to_page(addr);
        }
-        /* First we check that the Switcher won't overlap the fixmap area at
+        /*
+         * First we check that the Switcher won't overlap the fixmap area at
         * the top of memory.  It's currently nowhere near, but it could have
-         * very strange effects if it ever happened. */
+         * very strange effects if it ever happened.
+         */
        if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
                err = -ENOMEM;
                printk("lguest: mapping switcher would thwack fixmap\n");
                goto free_pages;
        }
-        /* Now we reserve the "virtual memory area" we want: 0xFFC00000
+        /*
+         * Now we reserve the "virtual memory area" we want: 0xFFC00000
         * (SWITCHER_ADDR).  We might not get it in theory, but in practice
         * it's worked so far.  The end address needs +1 because __get_vm_area
-         * allocates an extra guard page, so we need space for that. */
+         * allocates an extra guard page, so we need space for that.
+         */
        switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
                                     VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
                                     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
@@ -89,11 +101,13 @@ static __init int map_switcher(void)
                goto free_pages;
        }
-        /* This code actually sets up the pages we've allocated to appear at
+        /*
+         * This code actually sets up the pages we've allocated to appear at
         * SWITCHER_ADDR.  map_vm_area() takes the vma we allocated above, the
         * kind of pages we're mapping (kernel pages), and a pointer to our
         * array of struct pages.  It increments that pointer, but we don't
-         * care. */
+         * care.
+         */
        pagep = switcher_page;
        err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
        if (err) {
@@ -101,8 +115,10 @@ static __init int map_switcher(void)
                goto free_vma;
        }
-        /* Now the Switcher is mapped at the right address, we can't fail!
+        /*
-         * Copy in the compiled-in Switcher code (from <arch>_switcher.S). */
+         * Now the Switcher is mapped at the right address, we can't fail!
+         * Copy in the compiled-in Switcher code (from <arch>_switcher.S).
+         */
        memcpy(switcher_vma->addr, start_switcher_text,
               end_switcher_text - start_switcher_text);
@@ -124,8 +140,7 @@ out:
 }
 /*:*/
-/* Cleaning up the mapping when the module is unloaded is almost...
+/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
- * too easy. */
 static void unmap_switcher(void)
 {
        unsigned int i;
@@ -151,16 +166,19 @@ static void unmap_switcher(void)
 * But we can't trust the Guest: it might be trying to access the Launcher
 * code.  We have to check that the range is below the pfn_limit the Launcher
 * gave us.  We have to make sure that addr + len doesn't give us a false
- * positive by overflowing, too. */
+ * positive by overflowing, too.
+ */
 bool lguest_address_ok(const struct lguest *lg,
                       unsigned long addr, unsigned long len)
 {
        return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
 }
-/* This routine copies memory from the Guest.  Here we can see how useful the
+/*
+ * This routine copies memory from the Guest.  Here we can see how useful the
 * kill_lguest() routine we met in the Launcher can be: we return a random
- * value (all zeroes) instead of needing to return an error. */
+ * value (all zeroes) instead of needing to return an error.
+ */
 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 {
        if (!lguest_address_ok(cpu->lg, addr, bytes)
@@ -181,9 +199,11 @@ void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 }
 /*:*/
-/*H:030 Let's jump straight to the the main loop which runs the Guest.
+/*H:030
+ * Let's jump straight to the the main loop which runs the Guest.
 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
- * going around and around until something interesting happens. */
+ * going around and around until something interesting happens.
+ */
 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 {
        /* We stop running once the Guest is dead. */
@@ -195,10 +215,17 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                if (cpu->hcall)
                        do_hypercalls(cpu);
-                /* It's possible the Guest did a NOTIFY hypercall to the
+                /*
-                 * Launcher, in which case we return from the read() now. */
+                 * It's possible the Guest did a NOTIFY hypercall to the
+                 * Launcher.
+                 */
                if (cpu->pending_notify) {
+                        /*
+                         * Does it just needs to write to a registered
+                         * eventfd (ie. the appropriate virtqueue thread)?
+                         */
                        if (!send_notify_to_eventfd(cpu)) {
+                                /* OK, we tell the main Laucher. */
                                if (put_user(cpu->pending_notify, user))
                                        return -EFAULT;
                                return sizeof(cpu->pending_notify);
@@ -209,29 +236,39 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                if (signal_pending(current))
                        return -ERESTARTSYS;
-                /* Check if there are any interrupts which can be delivered now:
+                /*
+                 * Check if there are any interrupts which can be delivered now:
                 * if so, this sets up the hander to be executed when we next
-                 * run the Guest. */
+                 * run the Guest.
+                 */
                irq = interrupt_pending(cpu, &more);
                if (irq < LGUEST_IRQS)
                        try_deliver_interrupt(cpu, irq, more);
-                /* All long-lived kernel loops need to check with this horrible
+                /*
+                 * All long-lived kernel loops need to check with this horrible
                 * thing called the freezer.  If the Host is trying to suspend,
-                 * it stops us. */
+                 * it stops us.
+                 */
                try_to_freeze();
-                /* Just make absolutely sure the Guest is still alive.  One of
+                /*
-                 * those hypercalls could have been fatal, for example. */
+                 * Just make absolutely sure the Guest is still alive.  One of
+                 * those hypercalls could have been fatal, for example.
+                 */
                if (cpu->lg->dead)
                        break;
-                /* If the Guest asked to be stopped, we sleep.  The Guest's
+                /*
-                 * clock timer will wake us. */
+                 * If the Guest asked to be stopped, we sleep.  The Guest's
+                 * clock timer will wake us.
+                 */
                if (cpu->halted) {
                        set_current_state(TASK_INTERRUPTIBLE);
-                        /* Just before we sleep, make sure no interrupt snuck in
+                        /*
-                         * which we should be doing. */
+                         * Just before we sleep, make sure no interrupt snuck in
+                         * which we should be doing.
+                         */
                        if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
                                set_current_state(TASK_RUNNING);
                        else
@@ -239,8 +276,10 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                        continue;
                }
-                /* OK, now we're ready to jump into the Guest.  First we put up
+                /*
-                 * the "Do Not Disturb" sign: */
+                 * OK, now we're ready to jump into the Guest.  First we put up
+                 * the "Do Not Disturb" sign:
+                 */
                local_irq_disable();
                /* Actually run the Guest until something happens. */
@@ -327,8 +366,10 @@ static void __exit fini(void)
 }
 /*:*/
-/* The Host side of lguest can be a module.  This is a nice way for people to
+/*
- * play with it.  */
+ * The Host side of lguest can be a module.  This is a nice way for people to
+ * play with it.
+ */
 module_init(init);
 module_exit(fini);
 MODULE_LICENSE("GPL");
diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index c29ffa19cb74..83511eb0923d 100644
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -1,8 +1,10 @@
-/*P:500 Just as userspace programs request kernel operations through a system
+/*P:500
+ * Just as userspace programs request kernel operations through a system
 * call, the Guest requests Host operations through a "hypercall".  You might
 * notice this nomenclature doesn't really follow any logic, but the name has
 * been around for long enough that we're stuck with it.  As you'd expect, this
- * code is basically a one big switch statement. :*/
+ * code is basically a one big switch statement.
+:*/
 /*  Copyright (C) 2006 Rusty Russell IBM Corporation
@@ -28,30 +30,41 @@
 #include <asm/pgtable.h>
 #include "lg.h"
-/*H:120 This is the core hypercall routine: where the Guest gets what it wants.
+/*H:120
- * Or gets killed.  Or, in the case of LHCALL_SHUTDOWN, both. */
+ * This is the core hypercall routine: where the Guest gets what it wants.
+ * Or gets killed.  Or, in the case of LHCALL_SHUTDOWN, both.
+ */
 static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
 {
        switch (args->arg0) {
        case LHCALL_FLUSH_ASYNC:
-                /* This call does nothing, except by breaking out of the Guest
+                /*
-                 * it makes us process all the asynchronous hypercalls. */
+                 * This call does nothing, except by breaking out of the Guest
+                 * it makes us process all the asynchronous hypercalls.
+                 */
                break;
        case LHCALL_SEND_INTERRUPTS:
-                /* This call does nothing too, but by breaking out of the Guest
+                /*
-                 * it makes us process any pending interrupts. */
+                 * This call does nothing too, but by breaking out of the Guest
+                 * it makes us process any pending interrupts.
+                 */
                break;
        case LHCALL_LGUEST_INIT:
-                /* You can't get here unless you're already initialized.  Don't
+                /*
-                 * do that. */
+                 * You can't get here unless you're already initialized.  Don't
+                 * do that.
+                 */
                kill_guest(cpu, "already have lguest_data");
                break;
        case LHCALL_SHUTDOWN: {
-                /* Shutdown is such a trivial hypercall that we do it in four
-                 * lines right here. */
                char msg[128];
-                /* If the lgread fails, it will call kill_guest() itself; the
+                /*
-                 * kill_guest() with the message will be ignored. */
+                 * Shutdown is such a trivial hypercall that we do it in five
+                 * lines right here.
+                 *
+                 * If the lgread fails, it will call kill_guest() itself; the
+                 * kill_guest() with the message will be ignored.
+                 */
                __lgread(cpu, msg, args->arg1, sizeof(msg));
                msg[sizeof(msg)-1] = '\0';
                kill_guest(cpu, "CRASH: %s", msg);
@@ -60,16 +73,17 @@ static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
                break;
        }
        case LHCALL_FLUSH_TLB:
-                /* FLUSH_TLB comes in two flavors, depending on the
+                /* FLUSH_TLB comes in two flavors, depending on the argument: */
-                 * argument: */
                if (args->arg1)
                        guest_pagetable_clear_all(cpu);
                else
                        guest_pagetable_flush_user(cpu);
                break;
-        /* All these calls simply pass the arguments through to the right
+        /*
-         * routines. */
+         * All these calls simply pass the arguments through to the right
+         * routines.
+         */
        case LHCALL_NEW_PGTABLE:
                guest_new_pagetable(cpu, args->arg1);
                break;
@@ -112,15 +126,16 @@ static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
                        kill_guest(cpu, "Bad hypercall %li\n", args->arg0);
        }
 }
-/*:*/
-/*H:124 Asynchronous hypercalls are easy: we just look in the array in the
+/*H:124
+ * Asynchronous hypercalls are easy: we just look in the array in the
 * Guest's "struct lguest_data" to see if any new ones are marked "ready".
 *
 * We are careful to do these in order: obviously we respect the order the
 * Guest put them in the ring, but we also promise the Guest that they will
 * happen before any normal hypercall (which is why we check this before
- * checking for a normal hcall). */
+ * checking for a normal hcall).
+ */
 static void do_async_hcalls(struct lg_cpu *cpu)
 {
        unsigned int i;
@@ -133,22 +148,28 @@ static void do_async_hcalls(struct lg_cpu *cpu)
        /* We process "struct lguest_data"s hcalls[] ring once. */
        for (i = 0; i < ARRAY_SIZE(st); i++) {
                struct hcall_args args;
-                /* We remember where we were up to from last time.  This makes
+                /*
+                 * We remember where we were up to from last time.  This makes
                 * sure that the hypercalls are done in the order the Guest
-                 * places them in the ring. */
+                 * places them in the ring.
+                 */
                unsigned int n = cpu->next_hcall;
                /* 0xFF means there's no call here (yet). */
                if (st[n] == 0xFF)
                        break;
-                /* OK, we have hypercall.  Increment the "next_hcall" cursor,
+                /*
-                 * and wrap back to 0 if we reach the end. */
+                 * OK, we have hypercall.  Increment the "next_hcall" cursor,
+                 * and wrap back to 0 if we reach the end.
+                 */
                if (++cpu->next_hcall == LHCALL_RING_SIZE)
                        cpu->next_hcall = 0;
-                /* Copy the hypercall arguments into a local copy of
+                /*
-                 * the hcall_args struct. */
+                 * Copy the hypercall arguments into a local copy of the
+                 * hcall_args struct.
+                 */
                if (copy_from_user(&args, &cpu->lg->lguest_data->hcalls[n],
                                   sizeof(struct hcall_args))) {
                        kill_guest(cpu, "Fetching async hypercalls");
@@ -164,19 +185,25 @@ static void do_async_hcalls(struct lg_cpu *cpu)
                        break;
                }
-                /* Stop doing hypercalls if they want to notify the Launcher:
+                /*
-                 * it needs to service this first. */
+                 * Stop doing hypercalls if they want to notify the Launcher:
+                 * it needs to service this first.
+                 */
                if (cpu->pending_notify)
                        break;
        }
 }
-/* Last of all, we look at what happens first of all.  The very first time the
+/*
- * Guest makes a hypercall, we end up here to set things up: */
+ * Last of all, we look at what happens first of all.  The very first time the
+ * Guest makes a hypercall, we end up here to set things up:
+ */
 static void initialize(struct lg_cpu *cpu)
 {
-        /* You can't do anything until you're initialized.  The Guest knows the
+        /*
-         * rules, so we're unforgiving here. */
+         * You can't do anything until you're initialized.  The Guest knows the
+         * rules, so we're unforgiving here.
+         */
        if (cpu->hcall->arg0 != LHCALL_LGUEST_INIT) {
                kill_guest(cpu, "hypercall %li before INIT", cpu->hcall->arg0);
                return;
@@ -185,32 +212,44 @@ static void initialize(struct lg_cpu *cpu)
        if (lguest_arch_init_hypercalls(cpu))
                kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
-        /* The Guest tells us where we're not to deliver interrupts by putting
+        /*
-         * the range of addresses into "struct lguest_data". */
+         * The Guest tells us where we're not to deliver interrupts by putting
+         * the range of addresses into "struct lguest_data".
+         */
        if (get_user(cpu->lg->noirq_start, &cpu->lg->lguest_data->noirq_start)
            || get_user(cpu->lg->noirq_end, &cpu->lg->lguest_data->noirq_end))
                kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
-        /* We write the current time into the Guest's data page once so it can
+        /*
-         * set its clock. */
+         * We write the current time into the Guest's data page once so it can
+         * set its clock.
+         */
        write_timestamp(cpu);
        /* page_tables.c will also do some setup. */
        page_table_guest_data_init(cpu);
-        /* This is the one case where the above accesses might have been the
+        /*
+         * This is the one case where the above accesses might have been the
         * first write to a Guest page.  This may have caused a copy-on-write
         * fault, but the old page might be (read-only) in the Guest
-         * pagetable. */
+         * pagetable.
+         */
        guest_pagetable_clear_all(cpu);
 }
 /*:*/
-/*M:013 If a Guest reads from a page (so creates a mapping) that it has never
+/*M:013
+ * If a Guest reads from a page (so creates a mapping) that it has never
 * written to, and then the Launcher writes to it (ie. the output of a virtual
 * device), the Guest will still see the old page.  In practice, this never
 * happens: why would the Guest read a page which it has never written to?  But
- * a similar scenario might one day bite us, so it's worth mentioning. :*/
+ * a similar scenario might one day bite us, so it's worth mentioning.
+ *
+ * Note that if we used a shared anonymous mapping in the Launcher instead of
+ * mapping /dev/zero private, we wouldn't worry about cop-on-write.  And we
+ * need that to switch the Launcher to processes (away from threads) anyway.
+:*/
 /*H:100
 * Hypercalls
@@ -229,17 +268,22 @@ void do_hypercalls(struct lg_cpu *cpu)
                return;
        }
-        /* The Guest has initialized.
+        /*
+         * The Guest has initialized.
         *
-         * Look in the hypercall ring for the async hypercalls: */
+         * Look in the hypercall ring for the async hypercalls:
+         */
        do_async_hcalls(cpu);
-        /* If we stopped reading the hypercall ring because the Guest did a
+        /*
+         * If we stopped reading the hypercall ring because the Guest did a
         * NOTIFY to the Launcher, we want to return now.  Otherwise we do
-         * the hypercall. */
+         * the hypercall.
+         */
        if (!cpu->pending_notify) {
                do_hcall(cpu, cpu->hcall);
-                /* Tricky point: we reset the hcall pointer to mark the
+                /*
+                 * Tricky point: we reset the hcall pointer to mark the
                 * hypercall as "done".  We use the hcall pointer rather than
                 * the trap number to indicate a hypercall is pending.
                 * Normally it doesn't matter: the Guest will run again and
@@ -248,13 +292,16 @@ void do_hypercalls(struct lg_cpu *cpu)
                 * However, if we are signalled or the Guest sends I/O to the
                 * Launcher, the run_guest() loop will exit without running the
                 * Guest.  When it comes back it would try to re-run the
-                 * hypercall.  Finding that bug sucked. */
+                 * hypercall.  Finding that bug sucked.
+                 */
                cpu->hcall = NULL;
        }
 }
-/* This routine supplies the Guest with time: it's used for wallclock time at
+/*
- * initial boot and as a rough time source if the TSC isn't available. */
+ * This routine supplies the Guest with time: it's used for wallclock time at
+ * initial boot and as a rough time source if the TSC isn't available.
+ */
 void write_timestamp(struct lg_cpu *cpu)
 {
        struct timespec now;
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index 0e9067b0d507..18648180db02 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -1,4 +1,5 @@
-/*P:800 Interrupts (traps) are complicated enough to earn their own file.
+/*P:800
+ * Interrupts (traps) are complicated enough to earn their own file.
 * There are three classes of interrupts:
 *
 * 1) Real hardware interrupts which occur while we're running the Guest,
@@ -10,7 +11,8 @@
 * just like real hardware would deliver them.  Traps from the Guest can be set
 * up to go directly back into the Guest, but sometimes the Host wants to see
 * them first, so we also have a way of "reflecting" them into the Guest as if
- * they had been delivered to it directly. :*/
+ * they had been delivered to it directly.
+:*/
 #include <linux/uaccess.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
@@ -26,8 +28,10 @@ static unsigned long idt_address(u32 lo, u32 hi)
        return (lo & 0x0000FFFF) | (hi & 0xFFFF0000);
 }
-/* The "type" of the interrupt handler is a 4 bit field: we only support a
+/*
- * couple of types. */
+ * The "type" of the interrupt handler is a 4 bit field: we only support a
+ * couple of types.
+ */
 static int idt_type(u32 lo, u32 hi)
 {
        return (hi >> 8) & 0xF;
@@ -39,8 +43,10 @@ static bool idt_present(u32 lo, u32 hi)
        return (hi & 0x8000);
 }
-/* We need a helper to "push" a value onto the Guest's stack, since that's a
+/*
- * big part of what delivering an interrupt does. */
+ * We need a helper to "push" a value onto the Guest's stack, since that's a
+ * big part of what delivering an interrupt does.
+ */
 static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
 {
        /* Stack grows upwards: move stack then write value. */
@@ -48,7 +54,8 @@ static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
        lgwrite(cpu, *gstack, u32, val);
 }
-/*H:210 The set_guest_interrupt() routine actually delivers the interrupt or
+/*H:210
+ * The set_guest_interrupt() routine actually delivers the interrupt or
 * trap.  The mechanics of delivering traps and interrupts to the Guest are the
 * same, except some traps have an "error code" which gets pushed onto the
 * stack as well: the caller tells us if this is one.
@@ -59,7 +66,8 @@ static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
 *
 * We set up the stack just like the CPU does for a real interrupt, so it's
 * identical for the Guest (and the standard "iret" instruction will undo
- * it). */
+ * it).
+ */
 static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
                                bool has_err)
 {
@@ -67,20 +75,26 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
        u32 eflags, ss, irq_enable;
        unsigned long virtstack;
-        /* There are two cases for interrupts: one where the Guest is already
+        /*
+         * There are two cases for interrupts: one where the Guest is already
         * in the kernel, and a more complex one where the Guest is in
-         * userspace.  We check the privilege level to find out. */
+         * userspace.  We check the privilege level to find out.
+         */
        if ((cpu->regs->ss&0x3) != GUEST_PL) {
-                /* The Guest told us their kernel stack with the SET_STACK
+                /*
-                 * hypercall: both the virtual address and the segment */
+                 * The Guest told us their kernel stack with the SET_STACK
+                 * hypercall: both the virtual address and the segment.
+                 */
                virtstack = cpu->esp1;
                ss = cpu->ss1;
                origstack = gstack = guest_pa(cpu, virtstack);
-                /* We push the old stack segment and pointer onto the new
+                /*
+                 * We push the old stack segment and pointer onto the new
                 * stack: when the Guest does an "iret" back from the interrupt
                 * handler the CPU will notice they're dropping privilege
-                 * levels and expect these here. */
+                 * levels and expect these here.
+                 */
                push_guest_stack(cpu, &gstack, cpu->regs->ss);
                push_guest_stack(cpu, &gstack, cpu->regs->esp);
        } else {
@@ -91,18 +105,22 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
                origstack = gstack = guest_pa(cpu, virtstack);
        }
-        /* Remember that we never let the Guest actually disable interrupts, so
+        /*
+         * Remember that we never let the Guest actually disable interrupts, so
         * the "Interrupt Flag" bit is always set.  We copy that bit from the
         * Guest's "irq_enabled" field into the eflags word: we saw the Guest
-         * copy it back in "lguest_iret". */
+         * copy it back in "lguest_iret".
+         */
        eflags = cpu->regs->eflags;
        if (get_user(irq_enable, &cpu->lg->lguest_data->irq_enabled) == 0
            && !(irq_enable & X86_EFLAGS_IF))
                eflags &= ~X86_EFLAGS_IF;
-        /* An interrupt is expected to push three things on the stack: the old
+        /*
+         * An interrupt is expected to push three things on the stack: the old
         * "eflags" word, the old code segment, and the old instruction
-         * pointer. */
+         * pointer.
+         */
        push_guest_stack(cpu, &gstack, eflags);
        push_guest_stack(cpu, &gstack, cpu->regs->cs);
        push_guest_stack(cpu, &gstack, cpu->regs->eip);
@@ -111,15 +129,19 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
        if (has_err)
                push_guest_stack(cpu, &gstack, cpu->regs->errcode);
-        /* Now we've pushed all the old state, we change the stack, the code
+        /*
-         * segment and the address to execute. */
+         * Now we've pushed all the old state, we change the stack, the code
+         * segment and the address to execute.
+         */
        cpu->regs->ss = ss;
        cpu->regs->esp = virtstack + (gstack - origstack);
        cpu->regs->cs = (__KERNEL_CS|GUEST_PL);
        cpu->regs->eip = idt_address(lo, hi);
-        /* There are two kinds of interrupt handlers: 0xE is an "interrupt
+        /*
-         * gate" which expects interrupts to be disabled on entry. */
+         * There are two kinds of interrupt handlers: 0xE is an "interrupt
+         * gate" which expects interrupts to be disabled on entry.
+         */
        if (idt_type(lo, hi) == 0xE)
                if (put_user(0, &cpu->lg->lguest_data->irq_enabled))
                        kill_guest(cpu, "Disabling interrupts");
@@ -130,7 +152,8 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
 *
 * interrupt_pending() returns the first pending interrupt which isn't blocked
 * by the Guest.  It is called before every entry to the Guest, and just before
- * we go to sleep when the Guest has halted itself. */
+ * we go to sleep when the Guest has halted itself.
+ */
 unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
 {
        unsigned int irq;
@@ -140,8 +163,10 @@ unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
        if (!cpu->lg->lguest_data)
                return LGUEST_IRQS;
-        /* Take our "irqs_pending" array and remove any interrupts the Guest
+        /*
-         * wants blocked: the result ends up in "blk". */
+         * Take our "irqs_pending" array and remove any interrupts the Guest
+         * wants blocked: the result ends up in "blk".
+         */
        if (copy_from_user(&blk, cpu->lg->lguest_data->blocked_interrupts,
                           sizeof(blk)))
                return LGUEST_IRQS;
@@ -154,16 +179,20 @@ unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
        return irq;
 }
-/* This actually diverts the Guest to running an interrupt handler, once an
+/*
- * interrupt has been identified by interrupt_pending(). */
+ * This actually diverts the Guest to running an interrupt handler, once an
+ * interrupt has been identified by interrupt_pending().
+ */
 void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
 {
        struct desc_struct *idt;
        BUG_ON(irq >= LGUEST_IRQS);
-        /* They may be in the middle of an iret, where they asked us never to
+        /*
-         * deliver interrupts. */
+         * They may be in the middle of an iret, where they asked us never to
+         * deliver interrupts.
+         */
        if (cpu->regs->eip >= cpu->lg->noirq_start &&
           (cpu->regs->eip < cpu->lg->noirq_end))
                return;
@@ -187,29 +216,37 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
                }
        }
-        /* Look at the IDT entry the Guest gave us for this interrupt.  The
+        /*
+         * Look at the IDT entry the Guest gave us for this interrupt.  The
         * first 32 (FIRST_EXTERNAL_VECTOR) entries are for traps, so we skip
-         * over them. */
+         * over them.
+         */
        idt = &cpu->arch.idt[FIRST_EXTERNAL_VECTOR+irq];
        /* If they don't have a handler (yet?), we just ignore it */
        if (idt_present(idt->a, idt->b)) {
                /* OK, mark it no longer pending and deliver it. */
                clear_bit(irq, cpu->irqs_pending);
-                /* set_guest_interrupt() takes the interrupt descriptor and a
+                /*
+                 * set_guest_interrupt() takes the interrupt descriptor and a
                 * flag to say whether this interrupt pushes an error code onto
-                 * the stack as well: virtual interrupts never do. */
+                 * the stack as well: virtual interrupts never do.
+                 */
                set_guest_interrupt(cpu, idt->a, idt->b, false);
        }
-        /* Every time we deliver an interrupt, we update the timestamp in the
+        /*
+         * Every time we deliver an interrupt, we update the timestamp in the
         * Guest's lguest_data struct.  It would be better for the Guest if we
         * did this more often, but it can actually be quite slow: doing it
         * here is a compromise which means at least it gets updated every
-         * timer interrupt. */
+         * timer interrupt.
+         */
        write_timestamp(cpu);
-        /* If there are no other interrupts we want to deliver, clear
+        /*
-         * the pending flag. */
+         * If there are no other interrupts we want to deliver, clear
+         * the pending flag.
+         */
        if (!more)
                put_user(0, &cpu->lg->lguest_data->irq_pending);
 }
@@ -217,24 +254,29 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
 /* And this is the routine when we want to set an interrupt for the Guest. */
 void set_interrupt(struct lg_cpu *cpu, unsigned int irq)
 {
-        /* Next time the Guest runs, the core code will see if it can deliver
+        /*
-         * this interrupt. */
+         * Next time the Guest runs, the core code will see if it can deliver
+         * this interrupt.
+         */
        set_bit(irq, cpu->irqs_pending);
-        /* Make sure it sees it; it might be asleep (eg. halted), or
+        /*
-         * running the Guest right now, in which case kick_process()
+         * Make sure it sees it; it might be asleep (eg. halted), or running
-         * will knock it out. */
+         * the Guest right now, in which case kick_process() will knock it out.
+         */
        if (!wake_up_process(cpu->tsk))
                kick_process(cpu->tsk);
 }
 /*:*/
-/* Linux uses trap 128 for system calls.  Plan9 uses 64, and Ron Minnich sent
+/*
+ * Linux uses trap 128 for system calls.  Plan9 uses 64, and Ron Minnich sent
 * me a patch, so we support that too.  It'd be a big step for lguest if half
 * the Plan 9 user base were to start using it.
 *
 * Actually now I think of it, it's possible that Ron *is* half the Plan 9
- * userbase.  Oh well. */
+ * userbase.  Oh well.
+ */
 static bool could_be_syscall(unsigned int num)
 {
        /* Normal Linux SYSCALL_VECTOR or reserved vector? */
@@ -274,9 +316,11 @@ void free_interrupts(void)
                clear_bit(syscall_vector, used_vectors);
 }
-/*H:220 Now we've got the routines to deliver interrupts, delivering traps like
+/*H:220
+ * Now we've got the routines to deliver interrupts, delivering traps like
 * page fault is easy.  The only trick is that Intel decided that some traps
- * should have error codes: */
+ * should have error codes:
+ */
 static bool has_err(unsigned int trap)
 {
        return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17);
@@ -285,13 +329,17 @@ static bool has_err(unsigned int trap)
 /* deliver_trap() returns true if it could deliver the trap. */
 bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
 {
-        /* Trap numbers are always 8 bit, but we set an impossible trap number
+        /*
-         * for traps inside the Switcher, so check that here. */
+         * Trap numbers are always 8 bit, but we set an impossible trap number
+         * for traps inside the Switcher, so check that here.
+         */
        if (num >= ARRAY_SIZE(cpu->arch.idt))
                return false;
-        /* Early on the Guest hasn't set the IDT entries (or maybe it put a
+        /*
-         * bogus one in): if we fail here, the Guest will be killed. */
+         * Early on the Guest hasn't set the IDT entries (or maybe it put a
+         * bogus one in): if we fail here, the Guest will be killed.
+         */
        if (!idt_present(cpu->arch.idt[num].a, cpu->arch.idt[num].b))
                return false;
        set_guest_interrupt(cpu, cpu->arch.idt[num].a,
@@ -299,7 +347,8 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
        return true;
 }
-/*H:250 Here's the hard part: returning to the Host every time a trap happens
+/*H:250
+ * Here's the hard part: returning to the Host every time a trap happens
 * and then calling deliver_trap() and re-entering the Guest is slow.
 * Particularly because Guest userspace system calls are traps (usually trap
 * 128).
@@ -311,69 +360,87 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
 * the other hypervisors would beat it up at lunchtime.
 *
 * This routine indicates if a particular trap number could be delivered
- * directly. */
+ * directly.
+ */
 static bool direct_trap(unsigned int num)
 {
-        /* Hardware interrupts don't go to the Guest at all (except system
+        /*
-         * call). */
+         * Hardware interrupts don't go to the Guest at all (except system
+         * call).
+         */
        if (num >= FIRST_EXTERNAL_VECTOR && !could_be_syscall(num))
                return false;
-        /* The Host needs to see page faults (for shadow paging and to save the
+        /*
+         * The Host needs to see page faults (for shadow paging and to save the
         * fault address), general protection faults (in/out emulation) and
         * device not available (TS handling), invalid opcode fault (kvm hcall),
-         * and of course, the hypercall trap. */
+         * and of course, the hypercall trap.
+         */
        return num != 14 && num != 13 && num != 7 &&
                        num != 6 && num != LGUEST_TRAP_ENTRY;
 }
 /*:*/
-/*M:005 The Guest has the ability to turn its interrupt gates into trap gates,
+/*M:005
+ * The Guest has the ability to turn its interrupt gates into trap gates,
 * if it is careful.  The Host will let trap gates can go directly to the
 * Guest, but the Guest needs the interrupts atomically disabled for an
 * interrupt gate.  It can do this by pointing the trap gate at instructions
- * within noirq_start and noirq_end, where it can safely disable interrupts. */
+ * within noirq_start and noirq_end, where it can safely disable interrupts.
+ */
-/*M:006 The Guests do not use the sysenter (fast system call) instruction,
+/*M:006
+ * The Guests do not use the sysenter (fast system call) instruction,
 * because it's hardcoded to enter privilege level 0 and so can't go direct.
 * It's about twice as fast as the older "int 0x80" system call, so it might
 * still be worthwhile to handle it in the Switcher and lcall down to the
 * Guest.  The sysenter semantics are hairy tho: search for that keyword in
- * entry.S :*/
+ * entry.S
+:*/
-/*H:260 When we make traps go directly into the Guest, we need to make sure
+/*H:260
+ * When we make traps go directly into the Guest, we need to make sure
 * the kernel stack is valid (ie. mapped in the page tables).  Otherwise, the
 * CPU trying to deliver the trap will fault while trying to push the interrupt
 * words on the stack: this is called a double fault, and it forces us to kill
 * the Guest.
 *
- * Which is deeply unfair, because (literally!) it wasn't the Guests' fault. */
+ * Which is deeply unfair, because (literally!) it wasn't the Guests' fault.
+ */
 void pin_stack_pages(struct lg_cpu *cpu)
 {
        unsigned int i;
-        /* Depending on the CONFIG_4KSTACKS option, the Guest can have one or
+        /*
-         * two pages of stack space. */
+         * Depending on the CONFIG_4KSTACKS option, the Guest can have one or
+         * two pages of stack space.
+         */
        for (i = 0; i < cpu->lg->stack_pages; i++)
-                /* The stack grows *upwards*, so the address we're given is the
+                /*
+                 * The stack grows *upwards*, so the address we're given is the
                 * start of the page after the kernel stack.  Subtract one to
                 * get back onto the first stack page, and keep subtracting to
-                 * get to the rest of the stack pages. */
+                 * get to the rest of the stack pages.
+                 */
                pin_page(cpu, cpu->esp1 - 1 - i * PAGE_SIZE);
 }
-/* Direct traps also mean that we need to know whenever the Guest wants to use
+/*
+ * Direct traps also mean that we need to know whenever the Guest wants to use
 * a different kernel stack, so we can change the IDT entries to use that
 * stack.  The IDT entries expect a virtual address, so unlike most addresses
 * the Guest gives us, the "esp" (stack pointer) value here is virtual, not
 * physical.
 *
 * In Linux each process has its own kernel stack, so this happens a lot: we
- * change stacks on each context switch. */
+ * change stacks on each context switch.
+ */
 void guest_set_stack(struct lg_cpu *cpu, u32 seg, u32 esp, unsigned int pages)
 {
-        /* You are not allowed have a stack segment with privilege level 0: bad
+        /*
-         * Guest! */
+         * You're not allowed a stack segment with privilege level 0: bad Guest!
+         */
        if ((seg & 0x3) != GUEST_PL)
                kill_guest(cpu, "bad stack segment %i", seg);
        /* We only expect one or two stack pages. */
@@ -387,11 +454,15 @@ void guest_set_stack(struct lg_cpu *cpu, u32 seg, u32 esp, unsigned int pages)
        pin_stack_pages(cpu);
 }
-/* All this reference to mapping stacks leads us neatly into the other complex
+/*
- * part of the Host: page table handling. */
+ * All this reference to mapping stacks leads us neatly into the other complex
+ * part of the Host: page table handling.
+ */
-/*H:235 This is the routine which actually checks the Guest's IDT entry and
+/*H:235
- * transfers it into the entry in "struct lguest": */
+ * This is the routine which actually checks the Guest's IDT entry and
+ * transfers it into the entry in "struct lguest":
+ */
 static void set_trap(struct lg_cpu *cpu, struct desc_struct *trap,
                     unsigned int num, u32 lo, u32 hi)
 {
@@ -407,30 +478,38 @@ static void set_trap(struct lg_cpu *cpu, struct desc_struct *trap,
        if (type != 0xE && type != 0xF)
                kill_guest(cpu, "bad IDT type %i", type);
-        /* We only copy the handler address, present bit, privilege level and
+        /*
+         * We only copy the handler address, present bit, privilege level and
         * type.  The privilege level controls where the trap can be triggered
         * manually with an "int" instruction.  This is usually GUEST_PL,
-         * except for system calls which userspace can use. */
+         * except for system calls which userspace can use.
+         */
        trap->a = ((__KERNEL_CS|GUEST_PL)<<16) | (lo&0x0000FFFF);
        trap->b = (hi&0xFFFFEF00);
 }
-/*H:230 While we're here, dealing with delivering traps and interrupts to the
+/*H:230
+ * While we're here, dealing with delivering traps and interrupts to the
 * Guest, we might as well complete the picture: how the Guest tells us where
 * it wants them to go.  This would be simple, except making traps fast
 * requires some tricks.
 *
 * We saw the Guest setting Interrupt Descriptor Table (IDT) entries with the
- * LHCALL_LOAD_IDT_ENTRY hypercall before: that comes here. */
+ * LHCALL_LOAD_IDT_ENTRY hypercall before: that comes here.
+ */
 void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int num, u32 lo, u32 hi)
 {
-        /* Guest never handles: NMI, doublefault, spurious interrupt or
+        /*
-         * hypercall.  We ignore when it tries to set them. */
+         * Guest never handles: NMI, doublefault, spurious interrupt or
+         * hypercall.  We ignore when it tries to set them.
+         */
        if (num == 2 || num == 8 || num == 15 || num == LGUEST_TRAP_ENTRY)
                return;
-        /* Mark the IDT as changed: next time the Guest runs we'll know we have
+        /*
-         * to copy this again. */
+         * Mark the IDT as changed: next time the Guest runs we'll know we have
+         * to copy this again.
+         */
        cpu->changed |= CHANGED_IDT;
        /* Check that the Guest doesn't try to step outside the bounds. */
@@ -440,9 +519,11 @@ void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int num, u32 lo, u32 hi)
                set_trap(cpu, &cpu->arch.idt[num], num, lo, hi);
 }
-/* The default entry for each interrupt points into the Switcher routines which
+/*
+ * The default entry for each interrupt points into the Switcher routines which
 * simply return to the Host.  The run_guest() loop will then call
- * deliver_trap() to bounce it back into the Guest. */
+ * deliver_trap() to bounce it back into the Guest.
+ */
 static void default_idt_entry(struct desc_struct *idt,
                              int trap,
                              const unsigned long handler,
@@ -451,13 +532,17 @@ static void default_idt_entry(struct desc_struct *idt,
        /* A present interrupt gate. */
        u32 flags = 0x8e00;
-        /* Set the privilege level on the entry for the hypercall: this allows
+        /*
-         * the Guest to use the "int" instruction to trigger it. */
+         * Set the privilege level on the entry for the hypercall: this allows
+         * the Guest to use the "int" instruction to trigger it.
+         */
        if (trap == LGUEST_TRAP_ENTRY)
                flags |= (GUEST_PL << 13);
        else if (base)
-                /* Copy priv. level from what Guest asked for.  This allows
+                /*
-                 * debug (int 3) traps from Guest userspace, for example. */
+                 * Copy privilege level from what Guest asked for.  This allows
+                 * debug (int 3) traps from Guest userspace, for example.
+                 */
                flags |= (base->b & 0x6000);
        /* Now pack it into the IDT entry in its weird format. */
@@ -475,16 +560,20 @@ void setup_default_idt_entries(struct lguest_ro_state *state,
                default_idt_entry(&state->guest_idt[i], i, def[i], NULL);
 }
-/*H:240 We don't use the IDT entries in the "struct lguest" directly, instead
+/*H:240
+ * We don't use the IDT entries in the "struct lguest" directly, instead
 * we copy them into the IDT which we've set up for Guests on this CPU, just
- * before we run the Guest.  This routine does that copy. */
+ * before we run the Guest.  This routine does that copy.
+ */
 void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
                const unsigned long *def)
 {
        unsigned int i;
-        /* We can simply copy the direct traps, otherwise we use the default
+        /*
-         * ones in the Switcher: they will return to the Host. */
+         * We can simply copy the direct traps, otherwise we use the default
+         * ones in the Switcher: they will return to the Host.
+         */
        for (i = 0; i < ARRAY_SIZE(cpu->arch.idt); i++) {
                const struct desc_struct *gidt = &cpu->arch.idt[i];
@@ -492,14 +581,16 @@ void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
                if (!direct_trap(i))
                        continue;
-                /* Only trap gates (type 15) can go direct to the Guest.
+                /*
+                 * Only trap gates (type 15) can go direct to the Guest.
                 * Interrupt gates (type 14) disable interrupts as they are
                 * entered, which we never let the Guest do.  Not present
                 * entries (type 0x0) also can't go direct, of course.
                 *
                 * If it can't go direct, we still need to copy the priv. level:
                 * they might want to give userspace access to a software
-                 * interrupt. */
+                 * interrupt.
+                 */
                if (idt_type(gidt->a, gidt->b) == 0xF)
                        idt[i] = *gidt;
                else
@@ -518,7 +609,8 @@ void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
 * the next timer interrupt (in nanoseconds).  We use the high-resolution timer
 * infrastructure to set a callback at that time.
 *
- * 0 means "turn off the clock". */
+ * 0 means "turn off the clock".
+ */
 void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta)
 {
        ktime_t expires;
@@ -529,9 +621,11 @@ void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta)
                return;
        }
-        /* We use wallclock time here, so the Guest might not be running for
+        /*
+         * We use wallclock time here, so the Guest might not be running for
         * all the time between now and the timer interrupt it asked for.  This
-         * is almost always the right thing to do. */
+         * is almost always the right thing to do.
+         */
        expires = ktime_add_ns(ktime_get_real(), delta);
        hrtimer_start(&cpu->hrt, expires, HRTIMER_MODE_ABS);
 }
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 01c591923793..bc28745d05af 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -16,15 +16,13 @@
 void free_pagetables(void);
 int init_pagetables(struct page **switcher_page, unsigned int pages);
-struct pgdir
+struct pgdir {
-{
        unsigned long gpgdir;
        pgd_t *pgdir;
 };
 /* We have two pages shared with guests, per cpu.  */
-struct lguest_pages
+struct lguest_pages {
-{
        /* This is the stack page mapped rw in guest */
        char spare[PAGE_SIZE - sizeof(struct lguest_regs)];
        struct lguest_regs regs;
@@ -54,13 +52,13 @@ struct lg_cpu {
        unsigned long pending_notify; /* pfn from LHCALL_NOTIFY */
-        /* At end of a page shared mapped over lguest_pages in guest.  */
+        /* At end of a page shared mapped over lguest_pages in guest. */
        unsigned long regs_page;
        struct lguest_regs *regs;
        struct lguest_pages *last_pages;
-        int cpu_pgd; /* which pgd this cpu is currently using */
+        int cpu_pgd; /* Which pgd this cpu is currently using */
        /* If a hypercall was asked for, this points to the arguments. */
        struct hcall_args *hcall;
@@ -89,15 +87,17 @@ struct lg_eventfd_map {
 };
 /* The private info the thread maintains about the guest. */
-struct lguest
+struct lguest {
-{
        struct lguest_data __user *lguest_data;
        struct lg_cpu cpus[NR_CPUS];
        unsigned int nr_cpus;
        u32 pfn_limit;
-        /* This provides the offset to the base of guest-physical
-         * memory in the Launcher. */
+        /*
+         * This provides the offset to the base of guest-physical memory in the
+         * Launcher.
+         */
        void __user *mem_base;
        unsigned long kernel_address;
@@ -122,11 +122,13 @@ bool lguest_address_ok(const struct lguest *lg,
 void __lgread(struct lg_cpu *, void *, unsigned long, unsigned);
 void __lgwrite(struct lg_cpu *, unsigned long, const void *, unsigned);
-/*H:035 Using memory-copy operations like that is usually inconvient, so we
+/*H:035
+ * Using memory-copy operations like that is usually inconvient, so we
 * have the following helper macros which read and write a specific type (often
 * an unsigned long).
 *
- * This reads into a variable of the given type then returns that. */
+ * This reads into a variable of the given type then returns that.
+ */
 #define lgread(cpu, addr, type)                                         \
        ({ type _v; __lgread((cpu), &_v, (addr), sizeof(_v)); _v; })
@@ -140,9 +142,11 @@ void __lgwrite(struct lg_cpu *, unsigned long, const void *, unsigned);
 int run_guest(struct lg_cpu *cpu, unsigned long __user *user);
-/* Helper macros to obtain the first 12 or the last 20 bits, this is only the
+/*
+ * Helper macros to obtain the first 12 or the last 20 bits, this is only the
 * first step in the migration to the kernel types.  pte_pfn is already defined
- * in the kernel. */
+ * in the kernel.
+ */
 #define pgd_flags(x)    (pgd_val(x) & ~PAGE_MASK)
 #define pgd_pfn(x)      (pgd_val(x) >> PAGE_SHIFT)
 #define pmd_flags(x)    (pmd_val(x) & ~PAGE_MASK)
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index e082cdac88b4..b6200bc39b58 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -1,10 +1,12 @@
-/*P:050 Lguest guests use a very simple method to describe devices.  It's a
+/*P:050
+ * Lguest guests use a very simple method to describe devices.  It's a
 * series of device descriptors contained just above the top of normal Guest
 * memory.
 *
 * We use the standard "virtio" device infrastructure, which provides us with a
 * console, a network and a block driver.  Each one expects some configuration
- * information and a "virtqueue" or two to send and receive data. :*/
+ * information and a "virtqueue" or two to send and receive data.
+:*/
 #include <linux/init.h>
 #include <linux/bootmem.h>
 #include <linux/lguest_launcher.h>
@@ -20,8 +22,10 @@
 /* The pointer to our (page) of device descriptions. */
 static void *lguest_devices;
-/* For Guests, device memory can be used as normal memory, so we cast away the
+/*
- * __iomem to quieten sparse. */
+ * For Guests, device memory can be used as normal memory, so we cast away the
+ * __iomem to quieten sparse.
+ */
 static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
 {
        return (__force void *)ioremap_cache(phys_addr, PAGE_SIZE*pages);
@@ -32,8 +36,10 @@ static inline void lguest_unmap(void *addr)
        iounmap((__force void __iomem *)addr);
 }
-/*D:100 Each lguest device is just a virtio device plus a pointer to its entry
+/*D:100
- * in the lguest_devices page. */
+ * Each lguest device is just a virtio device plus a pointer to its entry
+ * in the lguest_devices page.
+ */
 struct lguest_device {
        struct virtio_device vdev;
@@ -41,9 +47,11 @@ struct lguest_device {
        struct lguest_device_desc *desc;
 };
-/* Since the virtio infrastructure hands us a pointer to the virtio_device all
+/*
+ * Since the virtio infrastructure hands us a pointer to the virtio_device all
 * the time, it helps to have a curt macro to get a pointer to the struct
- * lguest_device it's enclosed in.  */
+ * lguest_device it's enclosed in.
+ */
 #define to_lgdev(vd) container_of(vd, struct lguest_device, vdev)
 /*D:130
@@ -55,7 +63,8 @@ struct lguest_device {
 * the driver will look at them during setup.
 *
 * A convenient routine to return the device's virtqueue config array:
- * immediately after the descriptor. */
+ * immediately after the descriptor.
+ */
 static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
 {
        return (void *)(desc + 1);
@@ -98,10 +107,12 @@ static u32 lg_get_features(struct virtio_device *vdev)
        return features;
 }
-/* The virtio core takes the features the Host offers, and copies the
+/*
- * ones supported by the driver into the vdev->features array.  Once
+ * The virtio core takes the features the Host offers, and copies the ones
- * that's all sorted out, this routine is called so we can tell the
+ * supported by the driver into the vdev->features array.  Once that's all
- * Host which features we understand and accept. */
+ * sorted out, this routine is called so we can tell the Host which features we
+ * understand and accept.
+ */
 static void lg_finalize_features(struct virtio_device *vdev)
 {
        unsigned int i, bits;
@@ -112,10 +123,11 @@ static void lg_finalize_features(struct virtio_device *vdev)
        /* Give virtio_ring a chance to accept features. */
        vring_transport_features(vdev);
-        /* The vdev->feature array is a Linux bitmask: this isn't the
+        /*
-         * same as a the simple array of bits used by lguest devices
+         * The vdev->feature array is a Linux bitmask: this isn't the same as a
-         * for features.  So we do this slow, manual conversion which is
+         * the simple array of bits used by lguest devices for features.  So we
-         * completely general. */
+         * do this slow, manual conversion which is completely general.
+         */
        memset(out_features, 0, desc->feature_len);
        bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
        for (i = 0; i < bits; i++) {
@@ -146,15 +158,19 @@ static void lg_set(struct virtio_device *vdev, unsigned int offset,
        memcpy(lg_config(desc) + offset, buf, len);
 }
-/* The operations to get and set the status word just access the status field
+/*
- * of the device descriptor. */
+ * The operations to get and set the status word just access the status field
+ * of the device descriptor.
+ */
 static u8 lg_get_status(struct virtio_device *vdev)
 {
        return to_lgdev(vdev)->desc->status;
 }
-/* To notify on status updates, we (ab)use the NOTIFY hypercall, with the
+/*
- * descriptor address of the device.  A zero status means "reset". */
+ * To notify on status updates, we (ab)use the NOTIFY hypercall, with the
+ * descriptor address of the device.  A zero status means "reset".
+ */
 static void set_status(struct virtio_device *vdev, u8 status)
 {
        unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
@@ -191,8 +207,7 @@ static void lg_reset(struct virtio_device *vdev)
 */
 /*D:140 This is the information we remember about each virtqueue. */
-struct lguest_vq_info
+struct lguest_vq_info {
-{
        /* A copy of the information contained in the device config. */
        struct lguest_vqconfig config;
@@ -200,13 +215,17 @@ struct lguest_vq_info
        void *pages;
 };
-/* When the virtio_ring code wants to prod the Host, it calls us here and we
+/*
+ * When the virtio_ring code wants to prod the Host, it calls us here and we
 * make a hypercall.  We hand the physical address of the virtqueue so the Host
- * knows which virtqueue we're talking about. */
+ * knows which virtqueue we're talking about.
+ */
 static void lg_notify(struct virtqueue *vq)
 {
-        /* We store our virtqueue information in the "priv" pointer of the
+        /*
-         * virtqueue structure. */
+         * We store our virtqueue information in the "priv" pointer of the
+         * virtqueue structure.
+         */
        struct lguest_vq_info *lvq = vq->priv;
        kvm_hypercall1(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT);
@@ -215,7 +234,8 @@ static void lg_notify(struct virtqueue *vq)
 /* An extern declaration inside a C file is bad form.  Don't do it. */
 extern void lguest_setup_irq(unsigned int irq);
-/* This routine finds the first virtqueue described in the configuration of
+/*
+ * This routine finds the Nth virtqueue described in the configuration of
 * this device and sets it up.
 *
 * This is kind of an ugly duckling.  It'd be nicer to have a standard
@@ -223,9 +243,7 @@ extern void lguest_setup_irq(unsigned int irq);
 * everyone wants to do it differently.  The KVM coders want the Guest to
 * allocate its own pages and tell the Host where they are, but for lguest it's
 * simpler for the Host to simply tell us where the pages are.
- *
+ */
- * So we provide drivers with a "find the Nth virtqueue and set it up"
- * function. */
 static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
                                    unsigned index,
                                    void (*callback)(struct virtqueue *vq),
@@ -244,9 +262,11 @@ static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
        if (!lvq)
                return ERR_PTR(-ENOMEM);
-        /* Make a copy of the "struct lguest_vqconfig" entry, which sits after
+        /*
+         * Make a copy of the "struct lguest_vqconfig" entry, which sits after
         * the descriptor.  We need a copy because the config space might not
-         * be aligned correctly. */
+         * be aligned correctly.
+         */
        memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));
        printk("Mapping virtqueue %i addr %lx\n", index,
@@ -261,8 +281,10 @@ static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
                goto free_lvq;
        }
-        /* OK, tell virtio_ring.c to set up a virtqueue now we know its size
+        /*
-         * and we've got a pointer to its pages. */
+         * OK, tell virtio_ring.c to set up a virtqueue now we know its size
+         * and we've got a pointer to its pages.
+         */
        vq = vring_new_virtqueue(lvq->config.num, LGUEST_VRING_ALIGN,
                                 vdev, lvq->pages, lg_notify, callback, name);
        if (!vq) {
@@ -273,18 +295,23 @@ static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
        /* Make sure the interrupt is allocated. */
        lguest_setup_irq(lvq->config.irq);
-        /* Tell the interrupt for this virtqueue to go to the virtio_ring
+        /*
-         * interrupt handler. */
+         * Tell the interrupt for this virtqueue to go to the virtio_ring
-        /* FIXME: We used to have a flag for the Host to tell us we could use
+         * interrupt handler.
+         *
+         * FIXME: We used to have a flag for the Host to tell us we could use
         * the interrupt as a source of randomness: it'd be nice to have that
-         * back.. */
+         * back.
+         */
        err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
                          dev_name(&vdev->dev), vq);
        if (err)
                goto destroy_vring;
-        /* Last of all we hook up our 'struct lguest_vq_info" to the
+        /*
-         * virtqueue's priv pointer. */
+         * Last of all we hook up our 'struct lguest_vq_info" to the
+         * virtqueue's priv pointer.
+         */
        vq->priv = lvq;
        return vq;
@@ -358,11 +385,14 @@ static struct virtio_config_ops lguest_config_ops = {
        .del_vqs = lg_del_vqs,
 };
-/* The root device for the lguest virtio devices.  This makes them appear as
+/*
- * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2. */
+ * The root device for the lguest virtio devices.  This makes them appear as
+ * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2.
+ */
 static struct device *lguest_root;
-/*D:120 This is the core of the lguest bus: actually adding a new device.
+/*D:120
+ * This is the core of the lguest bus: actually adding a new device.
 * It's a separate function because it's neater that way, and because an
 * earlier version of the code supported hotplug and unplug.  They were removed
 * early on because they were never used.
@@ -371,14 +401,14 @@ static struct device *lguest_root;
 *
 * It's worth reading this carefully: we start with a pointer to the new device
 * descriptor in the "lguest_devices" page, and the offset into the device
- * descriptor page so we can uniquely identify it if things go badly wrong. */
+ * descriptor page so we can uniquely identify it if things go badly wrong.
+ */
 static void add_lguest_device(struct lguest_device_desc *d,
                              unsigned int offset)
 {
        struct lguest_device *ldev;
-        /* Start with zeroed memory; Linux's device layer seems to count on
+        /* Start with zeroed memory; Linux's device layer counts on it. */
-         * it. */
        ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
        if (!ldev) {
                printk(KERN_EMERG "Cannot allocate lguest dev %u type %u\n",
@@ -388,17 +418,25 @@ static void add_lguest_device(struct lguest_device_desc *d,
        /* This devices' parent is the lguest/ dir. */
        ldev->vdev.dev.parent = lguest_root;
-        /* We have a unique device index thanks to the dev_index counter. */
+        /*
+         * The device type comes straight from the descriptor.  There's also a
+         * device vendor field in the virtio_device struct, which we leave as
+         * 0.
+         */
        ldev->vdev.id.device = d->type;
-        /* We have a simple set of routines for querying the device's
+        /*
-         * configuration information and setting its status. */
+         * We have a simple set of routines for querying the device's
+         * configuration information and setting its status.
+         */
        ldev->vdev.config = &lguest_config_ops;
        /* And we remember the device's descriptor for lguest_config_ops. */
        ldev->desc = d;
-        /* register_virtio_device() sets up the generic fields for the struct
+        /*
+         * register_virtio_device() sets up the generic fields for the struct
         * virtio_device and calls device_register().  This makes the bus
-         * infrastructure look for a matching driver. */
+         * infrastructure look for a matching driver.
+         */
        if (register_virtio_device(&ldev->vdev) != 0) {
                printk(KERN_ERR "Failed to register lguest dev %u type %u\n",
                       offset, d->type);
@@ -406,8 +444,10 @@ static void add_lguest_device(struct lguest_device_desc *d,
        }
 }
-/*D:110 scan_devices() simply iterates through the device page.  The type 0 is
+/*D:110
- * reserved to mean "end of devices". */
+ * scan_devices() simply iterates through the device page.  The type 0 is
+ * reserved to mean "end of devices".
+ */
 static void scan_devices(void)
 {
        unsigned int i;
@@ -426,7 +466,8 @@ static void scan_devices(void)
        }
 }
-/*D:105 Fairly early in boot, lguest_devices_init() is called to set up the
+/*D:105
+ * Fairly early in boot, lguest_devices_init() is called to set up the
 * lguest device infrastructure.  We check that we are a Guest by checking
 * pv_info.name: there are other ways of checking, but this seems most
 * obvious to me.
@@ -437,7 +478,8 @@ static void scan_devices(void)
 * correct sysfs incantation).
 *
 * Finally we call scan_devices() which adds all the devices found in the
- * lguest_devices page. */
+ * lguest_devices page.
+ */
 static int __init lguest_devices_init(void)
 {
        if (strcmp(pv_info.name, "lguest") != 0)
@@ -456,11 +498,13 @@ static int __init lguest_devices_init(void)
 /* We do this after core stuff, but before the drivers. */
 postcore_initcall(lguest_devices_init);
-/*D:150 At this point in the journey we used to now wade through the lguest
+/*D:150
+ * At this point in the journey we used to now wade through the lguest
 * devices themselves: net, block and console.  Since they're all now virtio
 * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
 * they're kind of boring.  But this does mean you'll never experience the
 * thrill of reading the forbidden love scene buried deep in the block driver.
 *
 * "make Launcher" beckons, where we answer questions like "Where do Guests
- * come from?", and "What do you do when someone asks for optimization?". */
+ * come from?", and "What do you do when someone asks for optimization?".
+ */
diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c
index 9f9a2953b383..b4d3f7ca554f 100644
--- a/drivers/lguest/lguest_user.c
+++ b/drivers/lguest/lguest_user.c
@@ -1,8 +1,9 @@
 /*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
 * controls and communicates with the Guest.  For example, the first write will
- * tell us the Guest's memory layout, pagetable, entry point and kernel address
+ * tell us the Guest's memory layout and entry point.  A read will run the
- * offset.  A read will run the Guest until something happens, such as a signal
+ * Guest until something happens, such as a signal or the Guest doing a NOTIFY
- * or the Guest doing a NOTIFY out to the Launcher. :*/
+ * out to the Launcher.
+:*/
 #include <linux/uaccess.h>
 #include <linux/miscdevice.h>
 #include <linux/fs.h>
@@ -11,14 +12,41 @@
 #include <linux/file.h>
 #include "lg.h"
+/*L:056
+ * Before we move on, let's jump ahead and look at what the kernel does when
+ * it needs to look up the eventfds.  That will complete our picture of how we
+ * use RCU.
+ *
+ * The notification value is in cpu->pending_notify: we return true if it went
+ * to an eventfd.
+ */
 bool send_notify_to_eventfd(struct lg_cpu *cpu)
 {
        unsigned int i;
        struct lg_eventfd_map *map;
-        /* lg->eventfds is RCU-protected */
+        /*
+         * This "rcu_read_lock()" helps track when someone is still looking at
+         * the (RCU-using) eventfds array.  It's not actually a lock at all;
+         * indeed it's a noop in many configurations.  (You didn't expect me to
+         * explain all the RCU secrets here, did you?)
+         */
        rcu_read_lock();
+        /*
+         * rcu_dereference is the counter-side of rcu_assign_pointer(); it
+         * makes sure we don't access the memory pointed to by
+         * cpu->lg->eventfds before cpu->lg->eventfds is set.  Sounds crazy,
+         * but Alpha allows this!  Paul McKenney points out that a really
+         * aggressive compiler could have the same effect:
+         *   http://lists.ozlabs.org/pipermail/lguest/2009-July/001560.html
+         *
+         * So play safe, use rcu_dereference to get the rcu-protected pointer:
+         */
        map = rcu_dereference(cpu->lg->eventfds);
+        /*
+         * Simple array search: even if they add an eventfd while we do this,
+         * we'll continue to use the old array and just won't see the new one.
+         */
        for (i = 0; i < map->num; i++) {
                if (map->map[i].addr == cpu->pending_notify) {
                        eventfd_signal(map->map[i].event, 1);
@@ -26,19 +54,50 @@ bool send_notify_to_eventfd(struct lg_cpu *cpu)
                        break;
                }
        }
+        /* We're done with the rcu-protected variable cpu->lg->eventfds. */
        rcu_read_unlock();
+        /* If we cleared the notification, it's because we found a match. */
        return cpu->pending_notify == 0;
 }
+/*L:055
+ * One of the more tricksy tricks in the Linux Kernel is a technique called
+ * Read Copy Update.  Since one point of lguest is to teach lguest journeyers
+ * about kernel coding, I use it here.  (In case you're curious, other purposes
+ * include learning about virtualization and instilling a deep appreciation for
+ * simplicity and puppies).
+ *
+ * We keep a simple array which maps LHCALL_NOTIFY values to eventfds, but we
+ * add new eventfds without ever blocking readers from accessing the array.
+ * The current Launcher only does this during boot, so that never happens.  But
+ * Read Copy Update is cool, and adding a lock risks damaging even more puppies
+ * than this code does.
+ *
+ * We allocate a brand new one-larger array, copy the old one and add our new
+ * element.  Then we make the lg eventfd pointer point to the new array.
+ * That's the easy part: now we need to free the old one, but we need to make
+ * sure no slow CPU somewhere is still looking at it.  That's what
+ * synchronize_rcu does for us: waits until every CPU has indicated that it has
+ * moved on to know it's no longer using the old one.
+ *
+ * If that's unclear, see http://en.wikipedia.org/wiki/Read-copy-update.
+ */
 static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
 {
        struct lg_eventfd_map *new, *old = lg->eventfds;
+        /*
+         * We don't allow notifications on value 0 anyway (pending_notify of
+         * 0 means "nothing pending").
+         */
        if (!addr)
                return -EINVAL;
-        /* Replace the old array with the new one, carefully: others can
+        /*
-         * be accessing it at the same time */
+         * Replace the old array with the new one, carefully: others can
+         * be accessing it at the same time.
+         */
        new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
                      GFP_KERNEL);
        if (!new)
@@ -52,22 +111,41 @@ static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
        new->map[new->num].addr = addr;
        new->map[new->num].event = eventfd_ctx_fdget(fd);
        if (IS_ERR(new->map[new->num].event)) {
+                int err =  PTR_ERR(new->map[new->num].event);
                kfree(new);
-                return PTR_ERR(new->map[new->num].event);
+                return err;
        }
        new->num++;
-        /* Now put new one in place. */
+        /*
+         * Now put new one in place: rcu_assign_pointer() is a fancy way of
+         * doing "lg->eventfds = new", but it uses memory barriers to make
+         * absolutely sure that the contents of "new" written above is nailed
+         * down before we actually do the assignment.
+         *
+         * We have to think about these kinds of things when we're operating on
+         * live data without locks.
+         */
        rcu_assign_pointer(lg->eventfds, new);
-        /* We're not in a big hurry.  Wait until noone's looking at old
+        /*
-         * version, then delete it. */
+         * We're not in a big hurry.  Wait until noone's looking at old
+         * version, then free it.
+         */
        synchronize_rcu();
        kfree(old);
        return 0;
 }
+/*L:052
+ * Receiving notifications from the Guest is usually done by attaching a
+ * particular LHCALL_NOTIFY value to an event filedescriptor.  The eventfd will
+ * become readable when the Guest does an LHCALL_NOTIFY with that value.
+ *
+ * This is really convenient for processing each virtqueue in a separate
+ * thread.
+ */
 static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
 {
        unsigned long addr, fd;
@@ -79,15 +157,22 @@ static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
        if (get_user(fd, input) != 0)
                return -EFAULT;
+        /*
+         * Just make sure two callers don't add eventfds at once.  We really
+         * only need to lock against callers adding to the same Guest, so using
+         * the Big Lguest Lock is overkill.  But this is setup, not a fast path.
+         */
        mutex_lock(&lguest_lock);
        err = add_eventfd(lg, addr, fd);
        mutex_unlock(&lguest_lock);
-        return 0;
+        return err;
 }
-/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
+/*L:050
- * number to /dev/lguest. */
+ * Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
+ * number to /dev/lguest.
+ */
 static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
 {
        unsigned long irq;
@@ -97,12 +182,18 @@ static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
        if (irq >= LGUEST_IRQS)
                return -EINVAL;
+        /*
+         * Next time the Guest runs, the core code will see if it can deliver
+         * this interrupt.
+         */
        set_interrupt(cpu, irq);
        return 0;
 }
-/*L:040 Once our Guest is initialized, the Launcher makes it run by reading
+/*L:040
- * from /dev/lguest. */
+ * Once our Guest is initialized, the Launcher makes it run by reading
+ * from /dev/lguest.
+ */
 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
 {
        struct lguest *lg = file->private_data;
@@ -138,8 +229,10 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
                return len;
        }
-        /* If we returned from read() last time because the Guest sent I/O,
+        /*
-         * clear the flag. */
+         * If we returned from read() last time because the Guest sent I/O,
+         * clear the flag.
+         */
        if (cpu->pending_notify)
                cpu->pending_notify = 0;
@@ -147,8 +240,10 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
        return run_guest(cpu, (unsigned long __user *)user);
 }
-/*L:025 This actually initializes a CPU.  For the moment, a Guest is only
+/*L:025
- * uniprocessor, so "id" is always 0. */
+ * This actually initializes a CPU.  For the moment, a Guest is only
+ * uniprocessor, so "id" is always 0.
+ */
 static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
 {
        /* We have a limited number the number of CPUs in the lguest struct. */
@@ -163,8 +258,10 @@ static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
        /* Each CPU has a timer it can set. */
        init_clockdev(cpu);
-        /* We need a complete page for the Guest registers: they are accessible
+        /*
-         * to the Guest and we can only grant it access to whole pages. */
+         * We need a complete page for the Guest registers: they are accessible
+         * to the Guest and we can only grant it access to whole pages.
+         */
        cpu->regs_page = get_zeroed_page(GFP_KERNEL);
        if (!cpu->regs_page)
                return -ENOMEM;
@@ -172,29 +269,38 @@ static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
        /* We actually put the registers at the bottom of the page. */
        cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);
-        /* Now we initialize the Guest's registers, handing it the start
+        /*
-         * address. */
+         * Now we initialize the Guest's registers, handing it the start
+         * address.
+         */
        lguest_arch_setup_regs(cpu, start_ip);
-        /* We keep a pointer to the Launcher task (ie. current task) for when
+        /*
-         * other Guests want to wake this one (eg. console input). */
+         * We keep a pointer to the Launcher task (ie. current task) for when
+         * other Guests want to wake this one (eg. console input).
+         */
        cpu->tsk = current;
-        /* We need to keep a pointer to the Launcher's memory map, because if
+        /*
+         * We need to keep a pointer to the Launcher's memory map, because if
         * the Launcher dies we need to clean it up.  If we don't keep a
-         * reference, it is destroyed before close() is called. */
+         * reference, it is destroyed before close() is called.
+         */
        cpu->mm = get_task_mm(cpu->tsk);
-        /* We remember which CPU's pages this Guest used last, for optimization
+        /*
-         * when the same Guest runs on the same CPU twice. */
+         * We remember which CPU's pages this Guest used last, for optimization
+         * when the same Guest runs on the same CPU twice.
+         */
        cpu->last_pages = NULL;
        /* No error == success. */
        return 0;
 }
-/*L:020 The initialization write supplies 3 pointer sized (32 or 64 bit)
+/*L:020
- * values (in addition to the LHREQ_INITIALIZE value).  These are:
+ * The initialization write supplies 3 pointer sized (32 or 64 bit) values (in
+ * addition to the LHREQ_INITIALIZE value).  These are:
 *
 * base: The start of the Guest-physical memory inside the Launcher memory.
 *
@@ -206,14 +312,15 @@ static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
 */
 static int initialize(struct file *file, const unsigned long __user *input)
 {
-        /* "struct lguest" contains everything we (the Host) know about a
+        /* "struct lguest" contains all we (the Host) know about a Guest. */
-         * Guest. */
        struct lguest *lg;
        int err;
        unsigned long args[3];
-        /* We grab the Big Lguest lock, which protects against multiple
+        /*
-         * simultaneous initializations. */
+         * We grab the Big Lguest lock, which protects against multiple
+         * simultaneous initializations.
+         */
        mutex_lock(&lguest_lock);
        /* You can't initialize twice!  Close the device and start again... */
        if (file->private_data) {
@@ -248,8 +355,10 @@ static int initialize(struct file *file, const unsigned long __user *input)
        if (err)
                goto free_eventfds;
-        /* Initialize the Guest's shadow page tables, using the toplevel
+        /*
-         * address the Launcher gave us.  This allocates memory, so can fail. */
+         * Initialize the Guest's shadow page tables, using the toplevel
+         * address the Launcher gave us.  This allocates memory, so can fail.
+         */
        err = init_guest_pagetable(lg);
        if (err)
                goto free_regs;
@@ -274,20 +383,24 @@ unlock:
        return err;
 }
-/*L:010 The first operation the Launcher does must be a write.  All writes
+/*L:010
+ * The first operation the Launcher does must be a write.  All writes
 * start with an unsigned long number: for the first write this must be
 * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
- * writes of other values to send interrupts.
+ * writes of other values to send interrupts or set up receipt of notifications.
 *
 * Note that we overload the "offset" in the /dev/lguest file to indicate what
- * CPU number we're dealing with.  Currently this is always 0, since we only
+ * CPU number we're dealing with.  Currently this is always 0 since we only
 * support uniprocessor Guests, but you can see the beginnings of SMP support
- * here. */
+ * here.
+ */
 static ssize_t write(struct file *file, const char __user *in,
                     size_t size, loff_t *off)
 {
-        /* Once the Guest is initialized, we hold the "struct lguest" in the
+        /*
-         * file private data. */
+         * Once the Guest is initialized, we hold the "struct lguest" in the
+         * file private data.
+         */
        struct lguest *lg = file->private_data;
        const unsigned long __user *input = (const unsigned long __user *)in;
        unsigned long req;
@@ -322,13 +435,15 @@ static ssize_t write(struct file *file, const char __user *in,
        }
 }
-/*L:060 The final piece of interface code is the close() routine.  It reverses
+/*L:060
+ * The final piece of interface code is the close() routine.  It reverses
 * everything done in initialize().  This is usually called because the
 * Launcher exited.
 *
 * Note that the close routine returns 0 or a negative error number: it can't
 * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
- * letting them do it. :*/
+ * letting them do it.
+:*/
 static int close(struct inode *inode, struct file *file)
 {
        struct lguest *lg = file->private_data;
@@ -338,8 +453,10 @@ static int close(struct inode *inode, struct file *file)
        if (!lg)
                return 0;
-        /* We need the big lock, to protect from inter-guest I/O and other
+        /*
-         * Launchers initializing guests. */
+         * We need the big lock, to protect from inter-guest I/O and other
+         * Launchers initializing guests.
+         */
        mutex_lock(&lguest_lock);
        /* Free up the shadow page tables for the Guest. */
@@ -350,8 +467,10 @@ static int close(struct inode *inode, struct file *file)
                hrtimer_cancel(&lg->cpus[i].hrt);
                /* We can free up the register page we allocated. */
                free_page(lg->cpus[i].regs_page);
-                /* Now all the memory cleanups are done, it's safe to release
+                /*
-                 * the Launcher's memory management structure. */
+                 * Now all the memory cleanups are done, it's safe to release
+                 * the Launcher's memory management structure.
+                 */
                mmput(lg->cpus[i].mm);
        }
@@ -360,8 +479,10 @@ static int close(struct inode *inode, struct file *file)
                eventfd_ctx_put(lg->eventfds->map[i].event);
        kfree(lg->eventfds);
-        /* If lg->dead doesn't contain an error code it will be NULL or a
+        /*
-         * kmalloc()ed string, either of which is ok to hand to kfree(). */
+         * If lg->dead doesn't contain an error code it will be NULL or a
+         * kmalloc()ed string, either of which is ok to hand to kfree().
+         */
        if (!IS_ERR(lg->dead))
                kfree(lg->dead);
        /* Free the memory allocated to the lguest_struct */
@@ -385,7 +506,8 @@ static int close(struct inode *inode, struct file *file)
 *
 * We begin our understanding with the Host kernel interface which the Launcher
 * uses: reading and writing a character device called /dev/lguest.  All the
- * work happens in the read(), write() and close() routines: */
+ * work happens in the read(), write() and close() routines:
+ */
 static struct file_operations lguest_fops = {
        .owner   = THIS_MODULE,
        .release = close,
@@ -393,8 +515,10 @@ static struct file_operations lguest_fops = {
        .read    = read,
 };
-/* This is a textbook example of a "misc" character device.  Populate a "struct
+/*
- * miscdevice" and register it with misc_register(). */
+ * This is a textbook example of a "misc" character device.  Populate a "struct
+ * miscdevice" and register it with misc_register().
+ */
 static struct miscdevice lguest_dev = {
        .minor  = MISC_DYNAMIC_MINOR,
        .name   = "lguest",
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index a6fe1abda240..a8d0aee3bc0e 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -1,9 +1,11 @@
-/*P:700 The pagetable code, on the other hand, still shows the scars of
+/*P:700
+ * The pagetable code, on the other hand, still shows the scars of
 * previous encounters.  It's functional, and as neat as it can be in the
 * circumstances, but be wary, for these things are subtle and break easily.
 * The Guest provides a virtual to physical mapping, but we can neither trust
 * it nor use it: we verify and convert it here then point the CPU to the
- * converted Guest pages when running the Guest. :*/
+ * converted Guest pages when running the Guest.
+:*/
 /* Copyright (C) Rusty Russell IBM Corporation 2006.
 * GPL v2 and any later version */
@@ -17,18 +19,20 @@
 #include <asm/bootparam.h>
 #include "lg.h"
-/*M:008 We hold reference to pages, which prevents them from being swapped.
+/*M:008
+ * We hold reference to pages, which prevents them from being swapped.
 * It'd be nice to have a callback in the "struct mm_struct" when Linux wants
 * to swap out.  If we had this, and a shrinker callback to trim PTE pages, we
- * could probably consider launching Guests as non-root. :*/
+ * could probably consider launching Guests as non-root.
+:*/
 /*H:300
 * The Page Table Code
 *
- * We use two-level page tables for the Guest.  If you're not entirely
+ * We use two-level page tables for the Guest, or three-level with PAE.  If
- * comfortable with virtual addresses, physical addresses and page tables then
+ * you're not entirely comfortable with virtual addresses, physical addresses
- * I recommend you review arch/x86/lguest/boot.c's "Page Table Handling" (with
+ * and page tables then I recommend you review arch/x86/lguest/boot.c's "Page
- * diagrams!).
+ * Table Handling" (with diagrams!).
 *
 * The Guest keeps page tables, but we maintain the actual ones here: these are
 * called "shadow" page tables.  Which is a very Guest-centric name: these are
@@ -45,16 +49,18 @@
 *  (v) Flushing (throwing away) page tables,
 *  (vi) Mapping the Switcher when the Guest is about to run,
 *  (vii) Setting up the page tables initially.
- :*/
+:*/
+/*
-/* 1024 entries in a page table page maps 1024 pages: 4MB.  The Switcher is
+ * The Switcher uses the complete top PTE page.  That's 1024 PTE entries (4MB)
- * conveniently placed at the top 4MB, so it uses a separate, complete PTE
+ * or 512 PTE entries with PAE (2MB).
- * page.  */
+ */
 #define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1)
-/* For PAE we need the PMD index as well. We use the last 2MB, so we
+/*
- * will need the last pmd entry of the last pmd page.  */
+ * For PAE we need the PMD index as well. We use the last 2MB, so we
+ * will need the last pmd entry of the last pmd page.
+ */
 #ifdef CONFIG_X86_PAE
 #define SWITCHER_PMD_INDEX      (PTRS_PER_PMD - 1)
 #define RESERVE_MEM             2U
@@ -64,14 +70,18 @@
 #define CHECK_GPGD_MASK         _PAGE_TABLE
 #endif
-/* We actually need a separate PTE page for each CPU.  Remember that after the
+/*
+ * We actually need a separate PTE page for each CPU.  Remember that after the
 * Switcher code itself comes two pages for each CPU, and we don't want this
- * CPU's guest to see the pages of any other CPU. */
+ * CPU's guest to see the pages of any other CPU.
+ */
 static DEFINE_PER_CPU(pte_t *, switcher_pte_pages);
 #define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu)
-/*H:320 The page table code is curly enough to need helper functions to keep it
+/*H:320
- * clear and clean.
+ * The page table code is curly enough to need helper functions to keep it
+ * clear and clean.  The kernel itself provides many of them; one advantage
+ * of insisting that the Guest and Host use the same CONFIG_PAE setting.
 *
 * There are two functions which return pointers to the shadow (aka "real")
 * page tables.
@@ -79,7 +89,8 @@ static DEFINE_PER_CPU(pte_t *, switcher_pte_pages);
 * spgd_addr() takes the virtual address and returns a pointer to the top-level
 * page directory entry (PGD) for that address.  Since we keep track of several
 * page tables, the "i" argument tells us which one we're interested in (it's
- * usually the current one). */
+ * usually the current one).
+ */
 static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
 {
        unsigned int index = pgd_index(vaddr);
@@ -96,9 +107,11 @@ static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr)
 }
 #ifdef CONFIG_X86_PAE
-/* This routine then takes the PGD entry given above, which contains the
+/*
+ * This routine then takes the PGD entry given above, which contains the
 * address of the PMD page.  It then returns a pointer to the PMD entry for the
- * given address. */
+ * given address.
+ */
 static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
 {
        unsigned int index = pmd_index(vaddr);
@@ -119,9 +132,11 @@ static pmd_t *spmd_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
 }
 #endif
-/* This routine then takes the page directory entry returned above, which
+/*
+ * This routine then takes the page directory entry returned above, which
 * contains the address of the page table entry (PTE) page.  It then returns a
- * pointer to the PTE entry for the given address. */
+ * pointer to the PTE entry for the given address.
+ */
 static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
 {
 #ifdef CONFIG_X86_PAE
@@ -139,8 +154,10 @@ static pte_t *spte_addr(struct lg_cpu *cpu, pgd_t spgd, unsigned long vaddr)
        return &page[pte_index(vaddr)];
 }
-/* These two functions just like the above two, except they access the Guest
+/*
- * page tables.  Hence they return a Guest address. */
+ * These functions are just like the above two, except they access the Guest
+ * page tables.  Hence they return a Guest address.
+ */
 static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
 {
        unsigned int index = vaddr >> (PGDIR_SHIFT);
@@ -148,6 +165,7 @@ static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr)
 }
 #ifdef CONFIG_X86_PAE
+/* Follow the PGD to the PMD. */
 static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr)
 {
        unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT;
@@ -155,6 +173,7 @@ static unsigned long gpmd_addr(pgd_t gpgd, unsigned long vaddr)
        return gpage + pmd_index(vaddr) * sizeof(pmd_t);
 }
+/* Follow the PMD to the PTE. */
 static unsigned long gpte_addr(struct lg_cpu *cpu,
                               pmd_t gpmd, unsigned long vaddr)
 {
@@ -164,6 +183,7 @@ static unsigned long gpte_addr(struct lg_cpu *cpu,
        return gpage + pte_index(vaddr) * sizeof(pte_t);
 }
 #else
+/* Follow the PGD to the PTE (no mid-level for !PAE). */
 static unsigned long gpte_addr(struct lg_cpu *cpu,
                                pgd_t gpgd, unsigned long vaddr)
 {
@@ -175,17 +195,21 @@ static unsigned long gpte_addr(struct lg_cpu *cpu,
 #endif
 /*:*/
-/*M:014 get_pfn is slow: we could probably try to grab batches of pages here as
+/*M:014
- * an optimization (ie. pre-faulting). :*/
+ * get_pfn is slow: we could probably try to grab batches of pages here as
+ * an optimization (ie. pre-faulting).
+:*/
-/*H:350 This routine takes a page number given by the Guest and converts it to
+/*H:350
+ * This routine takes a page number given by the Guest and converts it to
 * an actual, physical page number.  It can fail for several reasons: the
 * virtual address might not be mapped by the Launcher, the write flag is set
 * and the page is read-only, or the write flag was set and the page was
 * shared so had to be copied, but we ran out of memory.
 *
 * This holds a reference to the page, so release_pte() is careful to put that
- * back. */
+ * back.
+ */
 static unsigned long get_pfn(unsigned long virtpfn, int write)
 {
        struct page *page;
@@ -198,33 +222,41 @@ static unsigned long get_pfn(unsigned long virtpfn, int write)
        return -1UL;
 }
-/*H:340 Converting a Guest page table entry to a shadow (ie. real) page table
+/*H:340
+ * Converting a Guest page table entry to a shadow (ie. real) page table
 * entry can be a little tricky.  The flags are (almost) the same, but the
 * Guest PTE contains a virtual page number: the CPU needs the real page
- * number. */
+ * number.
+ */
 static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
 {
        unsigned long pfn, base, flags;
-        /* The Guest sets the global flag, because it thinks that it is using
+        /*
+         * The Guest sets the global flag, because it thinks that it is using
         * PGE.  We only told it to use PGE so it would tell us whether it was
         * flushing a kernel mapping or a userspace mapping.  We don't actually
-         * use the global bit, so throw it away. */
+         * use the global bit, so throw it away.
+         */
        flags = (pte_flags(gpte) & ~_PAGE_GLOBAL);
        /* The Guest's pages are offset inside the Launcher. */
        base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE;
-        /* We need a temporary "unsigned long" variable to hold the answer from
+        /*
+         * We need a temporary "unsigned long" variable to hold the answer from
         * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't
         * fit in spte.pfn.  get_pfn() finds the real physical number of the
-         * page, given the virtual number. */
+         * page, given the virtual number.
+         */
        pfn = get_pfn(base + pte_pfn(gpte), write);
        if (pfn == -1UL) {
                kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte));
-                /* When we destroy the Guest, we'll go through the shadow page
+                /*
+                 * When we destroy the Guest, we'll go through the shadow page
                 * tables and release_pte() them.  Make sure we don't think
-                 * this one is valid! */
+                 * this one is valid!
+                 */
                flags = 0;
        }
        /* Now we assemble our shadow PTE from the page number and flags. */
@@ -234,8 +266,10 @@ static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write)
 /*H:460 And to complete the chain, release_pte() looks like this: */
 static void release_pte(pte_t pte)
 {
-        /* Remember that get_user_pages_fast() took a reference to the page, in
+        /*
-         * get_pfn()?  We have to put it back now. */
+         * Remember that get_user_pages_fast() took a reference to the page, in
+         * get_pfn()?  We have to put it back now.
+         */
        if (pte_flags(pte) & _PAGE_PRESENT)
                put_page(pte_page(pte));
 }
@@ -273,7 +307,8 @@ static void check_gpmd(struct lg_cpu *cpu, pmd_t gpmd)
 * and return to the Guest without it knowing.
 *
 * If we fixed up the fault (ie. we mapped the address), this routine returns
- * true.  Otherwise, it was a real fault and we need to tell the Guest. */
+ * true.  Otherwise, it was a real fault and we need to tell the Guest.
+ */
 bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 {
        pgd_t gpgd;
@@ -282,6 +317,7 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
        pte_t gpte;
        pte_t *spte;
+        /* Mid level for PAE. */
 #ifdef CONFIG_X86_PAE
        pmd_t *spmd;
        pmd_t gpmd;
@@ -298,22 +334,26 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
        if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
                /* No shadow entry: allocate a new shadow PTE page. */
                unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
-                /* This is not really the Guest's fault, but killing it is
+                /*
-                 * simple for this corner case. */
+                 * This is not really the Guest's fault, but killing it is
+                 * simple for this corner case.
+                 */
                if (!ptepage) {
                        kill_guest(cpu, "out of memory allocating pte page");
                        return false;
                }
                /* We check that the Guest pgd is OK. */
                check_gpgd(cpu, gpgd);
-                /* And we copy the flags to the shadow PGD entry.  The page
+                /*
-                 * number in the shadow PGD is the page we just allocated. */
+                 * And we copy the flags to the shadow PGD entry.  The page
+                 * number in the shadow PGD is the page we just allocated.
+                 */
                set_pgd(spgd, __pgd(__pa(ptepage) | pgd_flags(gpgd)));
        }
 #ifdef CONFIG_X86_PAE
        gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
-        /* middle level not present?  We can't map it in. */
+        /* Middle level not present?  We can't map it in. */
        if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
                return false;
@@ -324,8 +364,10 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
                /* No shadow entry: allocate a new shadow PTE page. */
                unsigned long ptepage = get_zeroed_page(GFP_KERNEL);
-                /* This is not really the Guest's fault, but killing it is
+                /*
-                * simple for this corner case. */
+                 * This is not really the Guest's fault, but killing it is
+                 * simple for this corner case.
+                 */
                if (!ptepage) {
                        kill_guest(cpu, "out of memory allocating pte page");
                        return false;
@@ -334,27 +376,37 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
                /* We check that the Guest pmd is OK. */
                check_gpmd(cpu, gpmd);
-                /* And we copy the flags to the shadow PMD entry.  The page
+                /*
-                 * number in the shadow PMD is the page we just allocated. */
+                 * And we copy the flags to the shadow PMD entry.  The page
+                 * number in the shadow PMD is the page we just allocated.
+                 */
                native_set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags(gpmd)));
        }
-        /* OK, now we look at the lower level in the Guest page table: keep its
+        /*
-         * address, because we might update it later. */
+         * OK, now we look at the lower level in the Guest page table: keep its
+         * address, because we might update it later.
+         */
        gpte_ptr = gpte_addr(cpu, gpmd, vaddr);
 #else
-        /* OK, now we look at the lower level in the Guest page table: keep its
+        /*
-         * address, because we might update it later. */
+         * OK, now we look at the lower level in the Guest page table: keep its
+         * address, because we might update it later.
+         */
        gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
 #endif
+        /* Read the actual PTE value. */
        gpte = lgread(cpu, gpte_ptr, pte_t);
        /* If this page isn't in the Guest page tables, we can't page it in. */
        if (!(pte_flags(gpte) & _PAGE_PRESENT))
                return false;
-        /* Check they're not trying to write to a page the Guest wants
+        /*
-         * read-only (bit 2 of errcode == write). */
+         * Check they're not trying to write to a page the Guest wants
+         * read-only (bit 2 of errcode == write).
+         */
        if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW))
                return false;
@@ -362,8 +414,10 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
        if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER))
                return false;
-        /* Check that the Guest PTE flags are OK, and the page number is below
+        /*
-         * the pfn_limit (ie. not mapping the Launcher binary). */
+         * Check that the Guest PTE flags are OK, and the page number is below
+         * the pfn_limit (ie. not mapping the Launcher binary).
+         */
        check_gpte(cpu, gpte);
        /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */
@@ -373,29 +427,40 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
        /* Get the pointer to the shadow PTE entry we're going to set. */
        spte = spte_addr(cpu, *spgd, vaddr);
-        /* If there was a valid shadow PTE entry here before, we release it.
-         * This can happen with a write to a previously read-only entry. */
+        /*
+         * If there was a valid shadow PTE entry here before, we release it.
+         * This can happen with a write to a previously read-only entry.
+         */
        release_pte(*spte);
-        /* If this is a write, we insist that the Guest page is writable (the
+        /*
-         * final arg to gpte_to_spte()). */
+         * If this is a write, we insist that the Guest page is writable (the
+         * final arg to gpte_to_spte()).
+         */
        if (pte_dirty(gpte))
                *spte = gpte_to_spte(cpu, gpte, 1);
        else
-                /* If this is a read, don't set the "writable" bit in the page
+                /*
+                 * If this is a read, don't set the "writable" bit in the page
                 * table entry, even if the Guest says it's writable.  That way
                 * we will come back here when a write does actually occur, so
-                 * we can update the Guest's _PAGE_DIRTY flag. */
+                 * we can update the Guest's _PAGE_DIRTY flag.
+                 */
                native_set_pte(spte, gpte_to_spte(cpu, pte_wrprotect(gpte), 0));
-        /* Finally, we write the Guest PTE entry back: we've set the
+        /*
-         * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */
+         * Finally, we write the Guest PTE entry back: we've set the
+         * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
+         */
        lgwrite(cpu, gpte_ptr, pte_t, gpte);
-        /* The fault is fixed, the page table is populated, the mapping
+        /*
+         * The fault is fixed, the page table is populated, the mapping
         * manipulated, the result returned and the code complete.  A small
         * delay and a trace of alliteration are the only indications the Guest
-         * has that a page fault occurred at all. */
+         * has that a page fault occurred at all.
+         */
        return true;
 }
@@ -408,7 +473,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
 * mapped, so it's overkill.
 *
 * This is a quick version which answers the question: is this virtual address
- * mapped by the shadow page tables, and is it writable? */
+ * mapped by the shadow page tables, and is it writable?
+ */
 static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
 {
        pgd_t *spgd;
@@ -428,21 +494,26 @@ static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
                return false;
 #endif
-        /* Check the flags on the pte entry itself: it must be present and
+        /*
-         * writable. */
+         * Check the flags on the pte entry itself: it must be present and
+         * writable.
+         */
        flags = pte_flags(*(spte_addr(cpu, *spgd, vaddr)));
        return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
 }
-/* So, when pin_stack_pages() asks us to pin a page, we check if it's already
+/*
+ * So, when pin_stack_pages() asks us to pin a page, we check if it's already
 * in the page tables, and if not, we call demand_page() with error code 2
- * (meaning "write"). */
+ * (meaning "write").
+ */
 void pin_page(struct lg_cpu *cpu, unsigned long vaddr)
 {
        if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2))
                kill_guest(cpu, "bad stack page %#lx", vaddr);
 }
+/*:*/
 #ifdef CONFIG_X86_PAE
 static void release_pmd(pmd_t *spmd)
@@ -479,15 +550,21 @@ static void release_pgd(pgd_t *spgd)
 }
 #else /* !CONFIG_X86_PAE */
-/*H:450 If we chase down the release_pgd() code, it looks like this: */
+/*H:450
+ * If we chase down the release_pgd() code, the non-PAE version looks like
+ * this.  The PAE version is almost identical, but instead of calling
+ * release_pte it calls release_pmd(), which looks much like this.
+ */
 static void release_pgd(pgd_t *spgd)
 {
        /* If the entry's not present, there's nothing to release. */
        if (pgd_flags(*spgd) & _PAGE_PRESENT) {
                unsigned int i;
-                /* Converting the pfn to find the actual PTE page is easy: turn
+                /*
+                 * Converting the pfn to find the actual PTE page is easy: turn
                 * the page number into a physical address, then convert to a
-                 * virtual address (easy for kernel pages like this one). */
+                 * virtual address (easy for kernel pages like this one).
+                 */
                pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
                /* For each entry in the page, we might need to release it. */
                for (i = 0; i < PTRS_PER_PTE; i++)
@@ -499,9 +576,12 @@ static void release_pgd(pgd_t *spgd)
        }
 }
 #endif
-/*H:445 We saw flush_user_mappings() twice: once from the flush_user_mappings()
+/*H:445
+ * We saw flush_user_mappings() twice: once from the flush_user_mappings()
 * hypercall and once in new_pgdir() when we re-used a top-level pgdir page.
- * It simply releases every PTE page from 0 up to the Guest's kernel address. */
+ * It simply releases every PTE page from 0 up to the Guest's kernel address.
+ */
 static void flush_user_mappings(struct lguest *lg, int idx)
 {
        unsigned int i;
@@ -510,10 +590,12 @@ static void flush_user_mappings(struct lguest *lg, int idx)
                release_pgd(lg->pgdirs[idx].pgdir + i);
 }
-/*H:440 (v) Flushing (throwing away) page tables,
+/*H:440
+ * (v) Flushing (throwing away) page tables,
 *
 * The Guest has a hypercall to throw away the page tables: it's used when a
- * large number of mappings have been changed. */
+ * large number of mappings have been changed.
+ */
 void guest_pagetable_flush_user(struct lg_cpu *cpu)
 {
        /* Drop the userspace part of the current page table. */
@@ -551,9 +633,11 @@ unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
        return pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
 }
-/* We keep several page tables.  This is a simple routine to find the page
+/*
+ * We keep several page tables.  This is a simple routine to find the page
 * table (if any) corresponding to this top-level address the Guest has given
- * us. */
+ * us.
+ */
 static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
 {
        unsigned int i;
@@ -563,9 +647,11 @@ static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable)
        return i;
 }
-/*H:435 And this is us, creating the new page directory.  If we really do
+/*H:435
+ * And this is us, creating the new page directory.  If we really do
 * allocate a new one (and so the kernel parts are not there), we set
- * blank_pgdir. */
+ * blank_pgdir.
+ */
 static unsigned int new_pgdir(struct lg_cpu *cpu,
                              unsigned long gpgdir,
                              int *blank_pgdir)
@@ -575,8 +661,10 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
        pmd_t *pmd_table;
 #endif
-        /* We pick one entry at random to throw out.  Choosing the Least
+        /*
-         * Recently Used might be better, but this is easy. */
+         * We pick one entry at random to throw out.  Choosing the Least
+         * Recently Used might be better, but this is easy.
+         */
        next = random32() % ARRAY_SIZE(cpu->lg->pgdirs);
        /* If it's never been allocated at all before, try now. */
        if (!cpu->lg->pgdirs[next].pgdir) {
@@ -587,8 +675,10 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
                        next = cpu->cpu_pgd;
                else {
 #ifdef CONFIG_X86_PAE
-                        /* In PAE mode, allocate a pmd page and populate the
+                        /*
-                         * last pgd entry. */
+                         * In PAE mode, allocate a pmd page and populate the
+                         * last pgd entry.
+                         */
                        pmd_table = (pmd_t *)get_zeroed_page(GFP_KERNEL);
                        if (!pmd_table) {
                                free_page((long)cpu->lg->pgdirs[next].pgdir);
@@ -598,8 +688,10 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
                                set_pgd(cpu->lg->pgdirs[next].pgdir +
                                        SWITCHER_PGD_INDEX,
                                        __pgd(__pa(pmd_table) | _PAGE_PRESENT));
-                                /* This is a blank page, so there are no kernel
+                                /*
-                                 * mappings: caller must map the stack! */
+                                 * This is a blank page, so there are no kernel
+                                 * mappings: caller must map the stack!
+                                 */
                                *blank_pgdir = 1;
                        }
 #else
@@ -615,19 +707,23 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
        return next;
 }
-/*H:430 (iv) Switching page tables
+/*H:430
+ * (iv) Switching page tables
 *
 * Now we've seen all the page table setting and manipulation, let's see
 * what happens when the Guest changes page tables (ie. changes the top-level
- * pgdir).  This occurs on almost every context switch. */
+ * pgdir).  This occurs on almost every context switch.
+ */
 void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
 {
        int newpgdir, repin = 0;
        /* Look to see if we have this one already. */
        newpgdir = find_pgdir(cpu->lg, pgtable);
-        /* If not, we allocate or mug an existing one: if it's a fresh one,
+        /*
-         * repin gets set to 1. */
+         * If not, we allocate or mug an existing one: if it's a fresh one,
+         * repin gets set to 1.
+         */
        if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
                newpgdir = new_pgdir(cpu, pgtable, &repin);
        /* Change the current pgd index to the new one. */
@@ -637,9 +733,11 @@ void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
                pin_stack_pages(cpu);
 }
-/*H:470 Finally, a routine which throws away everything: all PGD entries in all
+/*H:470
+ * Finally, a routine which throws away everything: all PGD entries in all
 * the shadow page tables, including the Guest's kernel mappings.  This is used
- * when we destroy the Guest. */
+ * when we destroy the Guest.
+ */
 static void release_all_pagetables(struct lguest *lg)
 {
        unsigned int i, j;
@@ -656,8 +754,10 @@ static void release_all_pagetables(struct lguest *lg)
                        spgd = lg->pgdirs[i].pgdir + SWITCHER_PGD_INDEX;
                        pmdpage = __va(pgd_pfn(*spgd) << PAGE_SHIFT);
-                        /* And release the pmd entries of that pmd page,
+                        /*
-                         * except for the switcher pmd. */
+                         * And release the pmd entries of that pmd page,
+                         * except for the switcher pmd.
+                         */
                        for (k = 0; k < SWITCHER_PMD_INDEX; k++)
                                release_pmd(&pmdpage[k]);
 #endif
@@ -667,10 +767,12 @@ static void release_all_pagetables(struct lguest *lg)
                }
 }
-/* We also throw away everything when a Guest tells us it's changed a kernel
+/*
+ * We also throw away everything when a Guest tells us it's changed a kernel
 * mapping.  Since kernel mappings are in every page table, it's easiest to
 * throw them all away.  This traps the Guest in amber for a while as
- * everything faults back in, but it's rare. */
+ * everything faults back in, but it's rare.
+ */
 void guest_pagetable_clear_all(struct lg_cpu *cpu)
 {
        release_all_pagetables(cpu->lg);
@@ -678,15 +780,19 @@ void guest_pagetable_clear_all(struct lg_cpu *cpu)
        pin_stack_pages(cpu);
 }
 /*:*/
-/*M:009 Since we throw away all mappings when a kernel mapping changes, our
+/*M:009
+ * Since we throw away all mappings when a kernel mapping changes, our
 * performance sucks for guests using highmem.  In fact, a guest with
 * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is
 * usually slower than a Guest with less memory.
 *
 * This, of course, cannot be fixed.  It would take some kind of... well, I
- * don't know, but the term "puissant code-fu" comes to mind. :*/
+ * don't know, but the term "puissant code-fu" comes to mind.
+:*/
-/*H:420 This is the routine which actually sets the page table entry for then
+/*H:420
+ * This is the routine which actually sets the page table entry for then
 * "idx"'th shadow page table.
 *
 * Normally, we can just throw out the old entry and replace it with 0: if they
@@ -715,31 +821,36 @@ static void do_set_pte(struct lg_cpu *cpu, int idx,
                spmd = spmd_addr(cpu, *spgd, vaddr);
                if (pmd_flags(*spmd) & _PAGE_PRESENT) {
 #endif
-                        /* Otherwise, we start by releasing
+                        /* Otherwise, start by releasing the existing entry. */
-                         * the existing entry. */
                        pte_t *spte = spte_addr(cpu, *spgd, vaddr);
                        release_pte(*spte);
-                        /* If they're setting this entry as dirty or accessed,
+                        /*
-                         * we might as well put that entry they've given us
+                         * If they're setting this entry as dirty or accessed,
-                         * in now.  This shaves 10% off a
+                         * we might as well put that entry they've given us in
-                         * copy-on-write micro-benchmark. */
+                         * now.  This shaves 10% off a copy-on-write
+                         * micro-benchmark.
+                         */
                        if (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) {
                                check_gpte(cpu, gpte);
                                native_set_pte(spte,
                                                gpte_to_spte(cpu, gpte,
                                                pte_flags(gpte) & _PAGE_DIRTY));
-                        } else
+                        } else {
-                                /* Otherwise kill it and we can demand_page()
+                                /*
-                                 * it in later. */
+                                 * Otherwise kill it and we can demand_page()
+                                 * it in later.
+                                 */
                                native_set_pte(spte, __pte(0));
+                        }
 #ifdef CONFIG_X86_PAE
                }
 #endif
        }
 }
-/*H:410 Updating a PTE entry is a little trickier.
+/*H:410
+ * Updating a PTE entry is a little trickier.
 *
 * We keep track of several different page tables (the Guest uses one for each
 * process, so it makes sense to cache at least a few).  Each of these have
@@ -748,12 +859,15 @@ static void do_set_pte(struct lg_cpu *cpu, int idx,
 * all the page tables, not just the current one.  This is rare.
 *
 * The benefit is that when we have to track a new page table, we can keep all
- * the kernel mappings.  This speeds up context switch immensely. */
+ * the kernel mappings.  This speeds up context switch immensely.
+ */
 void guest_set_pte(struct lg_cpu *cpu,
                   unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
 {
-        /* Kernel mappings must be changed on all top levels.  Slow, but doesn't
+        /*
-         * happen often. */
+         * Kernel mappings must be changed on all top levels.  Slow, but doesn't
+         * happen often.
+         */
        if (vaddr >= cpu->lg->kernel_address) {
                unsigned int i;
                for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
@@ -795,19 +909,25 @@ void guest_set_pgd(struct lguest *lg, unsigned long gpgdir, u32 idx)
                /* ... throw it away. */
                release_pgd(lg->pgdirs[pgdir].pgdir + idx);
 }
 #ifdef CONFIG_X86_PAE
+/* For setting a mid-level, we just throw everything away.  It's easy. */
 void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
 {
        guest_pagetable_clear_all(&lg->cpus[0]);
 }
 #endif
-/* Once we know how much memory we have we can construct simple identity
+/*H:505
- * (which set virtual == physical) and linear mappings
+ * To get through boot, we construct simple identity page mappings (which
- * which will get the Guest far enough into the boot to create its own.
+ * set virtual == physical) and linear mappings which will get the Guest far
+ * enough into the boot to create its own.  The linear mapping means we
+ * simplify the Guest boot, but it makes assumptions about their PAGE_OFFSET,
+ * as you'll see.
 *
 * We lay them out of the way, just below the initrd (which is why we need to
- * know its size here). */
+ * know its size here).
+ */
 static unsigned long setup_pagetables(struct lguest *lg,
                                      unsigned long mem,
                                      unsigned long initrd_size)
@@ -825,8 +945,10 @@ static unsigned long setup_pagetables(struct lguest *lg,
        unsigned int phys_linear;
 #endif
-        /* We have mapped_pages frames to map, so we need
+        /*
-         * linear_pages page tables to map them. */
+         * We have mapped_pages frames to map, so we need linear_pages page
+         * tables to map them.
+         */
        mapped_pages = mem / PAGE_SIZE;
        linear_pages = (mapped_pages + PTRS_PER_PTE - 1) / PTRS_PER_PTE;
@@ -837,10 +959,16 @@ static unsigned long setup_pagetables(struct lguest *lg,
        linear = (void *)pgdir - linear_pages * PAGE_SIZE;
 #ifdef CONFIG_X86_PAE
+        /*
+         * And the single mid page goes below that.  We only use one, but
+         * that's enough to map 1G, which definitely gets us through boot.
+         */
        pmds = (void *)linear - PAGE_SIZE;
 #endif
-        /* Linear mapping is easy: put every page's address into the
+        /*
-         * mapping in order. */
+         * Linear mapping is easy: put every page's address into the
+         * mapping in order.
+         */
        for (i = 0; i < mapped_pages; i++) {
                pte_t pte;
                pte = pfn_pte(i, __pgprot(_PAGE_PRESENT|_PAGE_RW|_PAGE_USER));
@@ -848,11 +976,14 @@ static unsigned long setup_pagetables(struct lguest *lg,
                        return -EFAULT;
        }
-        /* The top level points to the linear page table pages above.
-         * We setup the identity and linear mappings here. */
 #ifdef CONFIG_X86_PAE
+        /*
+         * Make the Guest PMD entries point to the corresponding place in the
+         * linear mapping (up to one page worth of PMD).
+         */
        for (i = j = 0; i < mapped_pages && j < PTRS_PER_PMD;
             i += PTRS_PER_PTE, j++) {
+                /* FIXME: native_set_pmd is overkill here. */
                native_set_pmd(&pmd, __pmd(((unsigned long)(linear + i)
                - mem_base) | _PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
@@ -860,18 +991,36 @@ static unsigned long setup_pagetables(struct lguest *lg,
                        return -EFAULT;
        }
+        /* One PGD entry, pointing to that PMD page. */
        set_pgd(&pgd, __pgd(((u32)pmds - mem_base) | _PAGE_PRESENT));
+        /* Copy it in as the first PGD entry (ie. addresses 0-1G). */
        if (copy_to_user(&pgdir[0], &pgd, sizeof(pgd)) != 0)
                return -EFAULT;
+        /*
+         * And the third PGD entry (ie. addresses 3G-4G).
+         *
+         * FIXME: This assumes that PAGE_OFFSET for the Guest is 0xC0000000.
+         */
        if (copy_to_user(&pgdir[3], &pgd, sizeof(pgd)) != 0)
                return -EFAULT;
 #else
+        /*
+         * The top level points to the linear page table pages above.
+         * We setup the identity and linear mappings here.
+         */
        phys_linear = (unsigned long)linear - mem_base;
        for (i = 0; i < mapped_pages; i += PTRS_PER_PTE) {
                pgd_t pgd;
+                /*
+                 * Create a PGD entry which points to the right part of the
+                 * linear PTE pages.
+                 */
                pgd = __pgd((phys_linear + i * sizeof(pte_t)) |
                            (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
+                /*
+                 * Copy it into the PGD page at 0 and PAGE_OFFSET.
+                 */
                if (copy_to_user(&pgdir[i / PTRS_PER_PTE], &pgd, sizeof(pgd))
                    || copy_to_user(&pgdir[pgd_index(PAGE_OFFSET)
                                           + i / PTRS_PER_PTE],
@@ -880,15 +1029,19 @@ static unsigned long setup_pagetables(struct lguest *lg,
        }
 #endif
-        /* We return the top level (guest-physical) address: remember where
+        /*
-         * this is. */
+         * We return the top level (guest-physical) address: we remember where
+         * this is to write it into lguest_data when the Guest initializes.
+         */
        return (unsigned long)pgdir - mem_base;
 }
-/*H:500 (vii) Setting up the page tables initially.
+/*H:500
+ * (vii) Setting up the page tables initially.
 *
 * When a Guest is first created, the Launcher tells us where the toplevel of
- * its first page table is.  We set some things up here: */
+ * its first page table is.  We set some things up here:
+ */
 int init_guest_pagetable(struct lguest *lg)
 {
        u64 mem;
@@ -898,21 +1051,27 @@ int init_guest_pagetable(struct lguest *lg)
        pgd_t *pgd;
        pmd_t *pmd_table;
 #endif
-        /* Get the Guest memory size and the ramdisk size from the boot header
+        /*
-         * located at lg->mem_base (Guest address 0). */
+         * Get the Guest memory size and the ramdisk size from the boot header
+         * located at lg->mem_base (Guest address 0).
+         */
        if (copy_from_user(&mem, &boot->e820_map[0].size, sizeof(mem))
            || get_user(initrd_size, &boot->hdr.ramdisk_size))
                return -EFAULT;
-        /* We start on the first shadow page table, and give it a blank PGD
+        /*
-         * page. */
+         * We start on the first shadow page table, and give it a blank PGD
+         * page.
+         */
        lg->pgdirs[0].gpgdir = setup_pagetables(lg, mem, initrd_size);
        if (IS_ERR_VALUE(lg->pgdirs[0].gpgdir))
                return lg->pgdirs[0].gpgdir;
        lg->pgdirs[0].pgdir = (pgd_t *)get_zeroed_page(GFP_KERNEL);
        if (!lg->pgdirs[0].pgdir)
                return -ENOMEM;
 #ifdef CONFIG_X86_PAE
+        /* For PAE, we also create the initial mid-level. */
        pgd = lg->pgdirs[0].pgdir;
        pmd_table = (pmd_t *) get_zeroed_page(GFP_KERNEL);
        if (!pmd_table)
@@ -921,27 +1080,33 @@ int init_guest_pagetable(struct lguest *lg)
        set_pgd(pgd + SWITCHER_PGD_INDEX,
                __pgd(__pa(pmd_table) | _PAGE_PRESENT));
 #endif
+        /* This is the current page table. */
        lg->cpus[0].cpu_pgd = 0;
        return 0;
 }
-/* When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
+/*H:508 When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
 void page_table_guest_data_init(struct lg_cpu *cpu)
 {
        /* We get the kernel address: above this is all kernel memory. */
        if (get_user(cpu->lg->kernel_address,
                &cpu->lg->lguest_data->kernel_address)
-                /* We tell the Guest that it can't use the top 2 or 4 MB
+                /*
-                 * of virtual addresses used by the Switcher. */
+                 * We tell the Guest that it can't use the top 2 or 4 MB
+                 * of virtual addresses used by the Switcher.
+                 */
                || put_user(RESERVE_MEM * 1024 * 1024,
                        &cpu->lg->lguest_data->reserve_mem)
                || put_user(cpu->lg->pgdirs[0].gpgdir,
                        &cpu->lg->lguest_data->pgdir))
                kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
-        /* In flush_user_mappings() we loop from 0 to
+        /*
+         * In flush_user_mappings() we loop from 0 to
         * "pgd_index(lg->kernel_address)".  This assumes it won't hit the
-         * Switcher mappings, so check that now. */
+         * Switcher mappings, so check that now.
+         */
 #ifdef CONFIG_X86_PAE
        if (pgd_index(cpu->lg->kernel_address) == SWITCHER_PGD_INDEX &&
                pmd_index(cpu->lg->kernel_address) == SWITCHER_PMD_INDEX)
@@ -964,12 +1129,14 @@ void free_guest_pagetable(struct lguest *lg)
                free_page((long)lg->pgdirs[i].pgdir);
 }
-/*H:480 (vi) Mapping the Switcher when the Guest is about to run.
+/*H:480
+ * (vi) Mapping the Switcher when the Guest is about to run.
 *
 * The Switcher and the two pages for this CPU need to be visible in the
 * Guest (and not the pages for other CPUs).  We have the appropriate PTE pages
 * for each CPU already set up, we just need to hook them in now we know which
- * Guest is about to run on this CPU. */
+ * Guest is about to run on this CPU.
+ */
 void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
 {
        pte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages);
@@ -980,30 +1147,38 @@ void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages)
        pmd_t switcher_pmd;
        pmd_t *pmd_table;
+        /* FIXME: native_set_pmd is overkill here. */
        native_set_pmd(&switcher_pmd, pfn_pmd(__pa(switcher_pte_page) >>
                       PAGE_SHIFT, PAGE_KERNEL_EXEC));
+        /* Figure out where the pmd page is, by reading the PGD, and converting
+         * it to a virtual address. */
        pmd_table = __va(pgd_pfn(cpu->lg->
                        pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX])
                                                                << PAGE_SHIFT);
+        /* Now write it into the shadow page table. */
        native_set_pmd(&pmd_table[SWITCHER_PMD_INDEX], switcher_pmd);
 #else
        pgd_t switcher_pgd;
-        /* Make the last PGD entry for this Guest point to the Switcher's PTE
+        /*
-         * page for this CPU (with appropriate flags). */
+         * Make the last PGD entry for this Guest point to the Switcher's PTE
+         * page for this CPU (with appropriate flags).
+         */
        switcher_pgd = __pgd(__pa(switcher_pte_page) | __PAGE_KERNEL_EXEC);
        cpu->lg->pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd;
 #endif
-        /* We also change the Switcher PTE page.  When we're running the Guest,
+        /*
+         * We also change the Switcher PTE page.  When we're running the Guest,
         * we want the Guest's "regs" page to appear where the first Switcher
         * page for this CPU is.  This is an optimization: when the Switcher
         * saves the Guest registers, it saves them into the first page of this
         * CPU's "struct lguest_pages": if we make sure the Guest's register
         * page is already mapped there, we don't have to copy them out
-         * again. */
+         * again.
+         */
        pfn = __pa(cpu->regs_page) >> PAGE_SHIFT;
        native_set_pte(&regs_pte, pfn_pte(pfn, PAGE_KERNEL));
        native_set_pte(&switcher_pte_page[pte_index((unsigned long)pages)],
@@ -1019,10 +1194,12 @@ static void free_switcher_pte_pages(void)
                free_page((long)switcher_pte_page(i));
 }
-/*H:520 Setting up the Switcher PTE page for given CPU is fairly easy, given
+/*H:520
+ * Setting up the Switcher PTE page for given CPU is fairly easy, given
 * the CPU number and the "struct page"s for the Switcher code itself.
 *
- * Currently the Switcher is less than a page long, so "pages" is always 1. */
+ * Currently the Switcher is less than a page long, so "pages" is always 1.
+ */
 static __init void populate_switcher_pte_page(unsigned int cpu,
                                              struct page *switcher_page[],
                                              unsigned int pages)
@@ -1043,13 +1220,16 @@ static __init void populate_switcher_pte_page(unsigned int cpu,
        native_set_pte(&pte[i], pfn_pte(page_to_pfn(switcher_page[i]),
                         __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW)));
-        /* The second page contains the "struct lguest_ro_state", and is
+        /*
-         * read-only. */
+         * The second page contains the "struct lguest_ro_state", and is
+         * read-only.
+         */
        native_set_pte(&pte[i+1], pfn_pte(page_to_pfn(switcher_page[i+1]),
                           __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
 }
-/* We've made it through the page table code.  Perhaps our tired brains are
+/*
+ * We've made it through the page table code.  Perhaps our tired brains are
 * still processing the details, or perhaps we're simply glad it's over.
 *
 * If nothing else, note that all this complexity in juggling shadow page tables
@@ -1058,10 +1238,13 @@ static __init void populate_switcher_pte_page(unsigned int cpu,
 * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD
 * have implemented shadow page table support directly into hardware.
 *
- * There is just one file remaining in the Host. */
+ * There is just one file remaining in the Host.
+ */
-/*H:510 At boot or module load time, init_pagetables() allocates and populates
+/*H:510
- * the Switcher PTE page for each CPU. */
+ * At boot or module load time, init_pagetables() allocates and populates
+ * the Switcher PTE page for each CPU.
+ */
 __init int init_pagetables(struct page **switcher_page, unsigned int pages)
 {
        unsigned int i;
diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c
index 482ed5a18750..951c57b0a7e0 100644
--- a/drivers/lguest/segments.c
+++ b/drivers/lguest/segments.c
@@ -1,4 +1,5 @@
-/*P:600 The x86 architecture has segments, which involve a table of descriptors
+/*P:600
+ * The x86 architecture has segments, which involve a table of descriptors
 * which can be used to do funky things with virtual address interpretation.
 * We originally used to use segments so the Guest couldn't alter the
 * Guest<->Host Switcher, and then we had to trim Guest segments, and restore
@@ -8,7 +9,8 @@
 *
 * In these modern times, the segment handling code consists of simple sanity
 * checks, and the worst you'll experience reading this code is butterfly-rash
- * from frolicking through its parklike serenity. :*/
+ * from frolicking through its parklike serenity.
+:*/
 #include "lg.h"
 /*H:600
@@ -41,10 +43,12 @@
 * begin.
 */
-/* There are several entries we don't let the Guest set.  The TSS entry is the
+/*
+ * There are several entries we don't let the Guest set.  The TSS entry is the
 * "Task State Segment" which controls all kinds of delicate things.  The
 * LGUEST_CS and LGUEST_DS entries are reserved for the Switcher, and the
- * the Guest can't be trusted to deal with double faults. */
+ * the Guest can't be trusted to deal with double faults.
+ */
 static bool ignored_gdt(unsigned int num)
 {
        return (num == GDT_ENTRY_TSS
@@ -53,42 +57,52 @@ static bool ignored_gdt(unsigned int num)
                || num == GDT_ENTRY_DOUBLEFAULT_TSS);
 }
-/*H:630 Once the Guest gave us new GDT entries, we fix them up a little.  We
+/*H:630
+ * Once the Guest gave us new GDT entries, we fix them up a little.  We
 * don't care if they're invalid: the worst that can happen is a General
 * Protection Fault in the Switcher when it restores a Guest segment register
 * which tries to use that entry.  Then we kill the Guest for causing such a
- * mess: the message will be "unhandled trap 256". */
+ * mess: the message will be "unhandled trap 256".
+ */
 static void fixup_gdt_table(struct lg_cpu *cpu, unsigned start, unsigned end)
 {
        unsigned int i;
        for (i = start; i < end; i++) {
-                /* We never copy these ones to real GDT, so we don't care what
+                /*
-                 * they say */
+                 * We never copy these ones to real GDT, so we don't care what
+                 * they say
+                 */
                if (ignored_gdt(i))
                        continue;
-                /* Segment descriptors contain a privilege level: the Guest is
+                /*
+                 * Segment descriptors contain a privilege level: the Guest is
                 * sometimes careless and leaves this as 0, even though it's
-                 * running at privilege level 1.  If so, we fix it here. */
+                 * running at privilege level 1.  If so, we fix it here.
+                 */
                if ((cpu->arch.gdt[i].b & 0x00006000) == 0)
                        cpu->arch.gdt[i].b |= (GUEST_PL << 13);
-                /* Each descriptor has an "accessed" bit.  If we don't set it
+                /*
+                 * Each descriptor has an "accessed" bit.  If we don't set it
                 * now, the CPU will try to set it when the Guest first loads
                 * that entry into a segment register.  But the GDT isn't
-                 * writable by the Guest, so bad things can happen. */
+                 * writable by the Guest, so bad things can happen.
+                 */
                cpu->arch.gdt[i].b |= 0x00000100;
        }
 }
-/*H:610 Like the IDT, we never simply use the GDT the Guest gives us.  We keep
+/*H:610
+ * Like the IDT, we never simply use the GDT the Guest gives us.  We keep
 * a GDT for each CPU, and copy across the Guest's entries each time we want to
 * run the Guest on that CPU.
 *
 * This routine is called at boot or modprobe time for each CPU to set up the
 * constant GDT entries: the ones which are the same no matter what Guest we're
- * running. */
+ * running.
+ */
 void setup_default_gdt_entries(struct lguest_ro_state *state)
 {
        struct desc_struct *gdt = state->guest_gdt;
@@ -98,30 +112,37 @@ void setup_default_gdt_entries(struct lguest_ro_state *state)
        gdt[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
        gdt[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
-        /* The TSS segment refers to the TSS entry for this particular CPU.
+        /*
+         * The TSS segment refers to the TSS entry for this particular CPU.
         * Forgive the magic flags: the 0x8900 means the entry is Present, it's
         * privilege level 0 Available 386 TSS system segment, and the 0x67
-         * means Saturn is eclipsed by Mercury in the twelfth house. */
+         * means Saturn is eclipsed by Mercury in the twelfth house.
+         */
        gdt[GDT_ENTRY_TSS].a = 0x00000067 | (tss << 16);
        gdt[GDT_ENTRY_TSS].b = 0x00008900 | (tss & 0xFF000000)
                | ((tss >> 16) & 0x000000FF);
 }
-/* This routine sets up the initial Guest GDT for booting.  All entries start
+/*
- * as 0 (unusable). */
+ * This routine sets up the initial Guest GDT for booting.  All entries start
+ * as 0 (unusable).
+ */
 void setup_guest_gdt(struct lg_cpu *cpu)
 {
-        /* Start with full 0-4G segments... */
+        /*
+         * Start with full 0-4G segments...except the Guest is allowed to use
+         * them, so set the privilege level appropriately in the flags.
+         */
        cpu->arch.gdt[GDT_ENTRY_KERNEL_CS] = FULL_EXEC_SEGMENT;
        cpu->arch.gdt[GDT_ENTRY_KERNEL_DS] = FULL_SEGMENT;
-        /* ...except the Guest is allowed to use them, so set the privilege
-         * level appropriately in the flags. */
        cpu->arch.gdt[GDT_ENTRY_KERNEL_CS].b |= (GUEST_PL << 13);
        cpu->arch.gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13);
 }
-/*H:650 An optimization of copy_gdt(), for just the three "thead-local storage"
+/*H:650
- * entries. */
+ * An optimization of copy_gdt(), for just the three "thead-local storage"
+ * entries.
+ */
 void copy_gdt_tls(const struct lg_cpu *cpu, struct desc_struct *gdt)
 {
        unsigned int i;
@@ -130,26 +151,34 @@ void copy_gdt_tls(const struct lg_cpu *cpu, struct desc_struct *gdt)
                gdt[i] = cpu->arch.gdt[i];
 }
-/*H:640 When the Guest is run on a different CPU, or the GDT entries have
+/*H:640
- * changed, copy_gdt() is called to copy the Guest's GDT entries across to this
+ * When the Guest is run on a different CPU, or the GDT entries have changed,
- * CPU's GDT. */
+ * copy_gdt() is called to copy the Guest's GDT entries across to this CPU's
+ * GDT.
+ */
 void copy_gdt(const struct lg_cpu *cpu, struct desc_struct *gdt)
 {
        unsigned int i;
-        /* The default entries from setup_default_gdt_entries() are not
+        /*
-         * replaced.  See ignored_gdt() above. */
+         * The default entries from setup_default_gdt_entries() are not
+         * replaced.  See ignored_gdt() above.
+         */
        for (i = 0; i < GDT_ENTRIES; i++)
                if (!ignored_gdt(i))
                        gdt[i] = cpu->arch.gdt[i];
 }
-/*H:620 This is where the Guest asks us to load a new GDT entry
+/*H:620
- * (LHCALL_LOAD_GDT_ENTRY).  We tweak the entry and copy it in. */
+ * This is where the Guest asks us to load a new GDT entry
+ * (LHCALL_LOAD_GDT_ENTRY).  We tweak the entry and copy it in.
+ */
 void load_guest_gdt_entry(struct lg_cpu *cpu, u32 num, u32 lo, u32 hi)
 {
-        /* We assume the Guest has the same number of GDT entries as the
+        /*
-         * Host, otherwise we'd have to dynamically allocate the Guest GDT. */
+         * We assume the Guest has the same number of GDT entries as the
+         * Host, otherwise we'd have to dynamically allocate the Guest GDT.
+         */
        if (num >= ARRAY_SIZE(cpu->arch.gdt))
                kill_guest(cpu, "too many gdt entries %i", num);
@@ -157,15 +186,19 @@ void load_guest_gdt_entry(struct lg_cpu *cpu, u32 num, u32 lo, u32 hi)
        cpu->arch.gdt[num].a = lo;
        cpu->arch.gdt[num].b = hi;
        fixup_gdt_table(cpu, num, num+1);
-        /* Mark that the GDT changed so the core knows it has to copy it again,
+        /*
-         * even if the Guest is run on the same CPU. */
+         * Mark that the GDT changed so the core knows it has to copy it again,
+         * even if the Guest is run on the same CPU.
+         */
        cpu->changed |= CHANGED_GDT;
 }
-/* This is the fast-track version for just changing the three TLS entries.
+/*
+ * This is the fast-track version for just changing the three TLS entries.
 * Remember that this happens on every context switch, so it's worth
 * optimizing.  But wouldn't it be neater to have a single hypercall to cover
- * both cases? */
+ * both cases?
+ */
 void guest_load_tls(struct lg_cpu *cpu, unsigned long gtls)
 {
        struct desc_struct *tls = &cpu->arch.gdt[GDT_ENTRY_TLS_MIN];
@@ -175,7 +208,6 @@ void guest_load_tls(struct lg_cpu *cpu, unsigned long gtls)
        /* Note that just the TLS entries have changed. */
        cpu->changed |= CHANGED_GDT_TLS;
 }
-/*:*/
 /*H:660
 * With this, we have finished the Host.
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index eaf722fe309a..6ae388849a3b 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -17,13 +17,15 @@
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
-/*P:450 This file contains the x86-specific lguest code.  It used to be all
+/*P:450
+ * This file contains the x86-specific lguest code.  It used to be all
 * mixed in with drivers/lguest/core.c but several foolhardy code slashers
 * wrestled most of the dependencies out to here in preparation for porting
 * lguest to other architectures (see what I mean by foolhardy?).
 *
 * This also contains a couple of non-obvious setup and teardown pieces which
- * were implemented after days of debugging pain. :*/
+ * were implemented after days of debugging pain.
+:*/
 #include <linux/kernel.h>
 #include <linux/start_kernel.h>
 #include <linux/string.h>
@@ -82,25 +84,33 @@ static DEFINE_PER_CPU(struct lg_cpu *, last_cpu);
 */
 static void copy_in_guest_info(struct lg_cpu *cpu, struct lguest_pages *pages)
 {
-        /* Copying all this data can be quite expensive.  We usually run the
+        /*
+         * Copying all this data can be quite expensive.  We usually run the
         * same Guest we ran last time (and that Guest hasn't run anywhere else
         * meanwhile).  If that's not the case, we pretend everything in the
-         * Guest has changed. */
+         * Guest has changed.
+         */
        if (__get_cpu_var(last_cpu) != cpu || cpu->last_pages != pages) {
                __get_cpu_var(last_cpu) = cpu;
                cpu->last_pages = pages;
                cpu->changed = CHANGED_ALL;
        }
-        /* These copies are pretty cheap, so we do them unconditionally: */
+        /*
-        /* Save the current Host top-level page directory. */
+         * These copies are pretty cheap, so we do them unconditionally: */
+        /* Save the current Host top-level page directory.
+         */
        pages->state.host_cr3 = __pa(current->mm->pgd);
-        /* Set up the Guest's page tables to see this CPU's pages (and no
+        /*
-         * other CPU's pages). */
+         * Set up the Guest's page tables to see this CPU's pages (and no
+         * other CPU's pages).
+         */
        map_switcher_in_guest(cpu, pages);
-        /* Set up the two "TSS" members which tell the CPU what stack to use
+        /*
+         * Set up the two "TSS" members which tell the CPU what stack to use
         * for traps which do directly into the Guest (ie. traps at privilege
-         * level 1). */
+         * level 1).
+         */
        pages->state.guest_tss.sp1 = cpu->esp1;
        pages->state.guest_tss.ss1 = cpu->ss1;
@@ -125,97 +135,126 @@ static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages)
        /* This is a dummy value we need for GCC's sake. */
        unsigned int clobber;
-        /* Copy the guest-specific information into this CPU's "struct
+        /*
-         * lguest_pages". */
+         * Copy the guest-specific information into this CPU's "struct
+         * lguest_pages".
+         */
        copy_in_guest_info(cpu, pages);
-        /* Set the trap number to 256 (impossible value).  If we fault while
+        /*
+         * Set the trap number to 256 (impossible value).  If we fault while
         * switching to the Guest (bad segment registers or bug), this will
-         * cause us to abort the Guest. */
+         * cause us to abort the Guest.
+         */
        cpu->regs->trapnum = 256;
-        /* Now: we push the "eflags" register on the stack, then do an "lcall".
+        /*
+         * Now: we push the "eflags" register on the stack, then do an "lcall".
         * This is how we change from using the kernel code segment to using
         * the dedicated lguest code segment, as well as jumping into the
         * Switcher.
         *
         * The lcall also pushes the old code segment (KERNEL_CS) onto the
         * stack, then the address of this call.  This stack layout happens to
-         * exactly match the stack layout created by an interrupt... */
+         * exactly match the stack layout created by an interrupt...
+         */
        asm volatile("pushf; lcall *lguest_entry"
-                     /* This is how we tell GCC that %eax ("a") and %ebx ("b")
+                     /*
-                      * are changed by this routine.  The "=" means output. */
+                      * This is how we tell GCC that %eax ("a") and %ebx ("b")
+                      * are changed by this routine.  The "=" means output.
+                      */
                     : "=a"(clobber), "=b"(clobber)
-                     /* %eax contains the pages pointer.  ("0" refers to the
+                     /*
+                      * %eax contains the pages pointer.  ("0" refers to the
                      * 0-th argument above, ie "a").  %ebx contains the
                      * physical address of the Guest's top-level page
-                      * directory. */
+                      * directory.
+                      */
                     : "0"(pages), "1"(__pa(cpu->lg->pgdirs[cpu->cpu_pgd].pgdir))
-                     /* We tell gcc that all these registers could change,
+                     /*
+                      * We tell gcc that all these registers could change,
                      * which means we don't have to save and restore them in
-                      * the Switcher. */
+                      * the Switcher.
+                      */
                     : "memory", "%edx", "%ecx", "%edi", "%esi");
 }
 /*:*/
-/*M:002 There are hooks in the scheduler which we can register to tell when we
+/*M:002
+ * There are hooks in the scheduler which we can register to tell when we
 * get kicked off the CPU (preempt_notifier_register()).  This would allow us
 * to lazily disable SYSENTER which would regain some performance, and should
 * also simplify copy_in_guest_info().  Note that we'd still need to restore
 * things when we exit to Launcher userspace, but that's fairly easy.
 *
- * We could also try using this hooks for PGE, but that might be too expensive.
+ * We could also try using these hooks for PGE, but that might be too expensive.
 *
- * The hooks were designed for KVM, but we can also put them to good use. :*/
+ * The hooks were designed for KVM, but we can also put them to good use.
+:*/
-/*H:040 This is the i386-specific code to setup and run the Guest.  Interrupts
+/*H:040
- * are disabled: we own the CPU. */
+ * This is the i386-specific code to setup and run the Guest.  Interrupts
+ * are disabled: we own the CPU.
+ */
 void lguest_arch_run_guest(struct lg_cpu *cpu)
 {
-        /* Remember the awfully-named TS bit?  If the Guest has asked to set it
+        /*
+         * Remember the awfully-named TS bit?  If the Guest has asked to set it
         * we set it now, so we can trap and pass that trap to the Guest if it
-         * uses the FPU. */
+         * uses the FPU.
+         */
        if (cpu->ts)
                unlazy_fpu(current);
-        /* SYSENTER is an optimized way of doing system calls.  We can't allow
+        /*
+         * SYSENTER is an optimized way of doing system calls.  We can't allow
         * it because it always jumps to privilege level 0.  A normal Guest
         * won't try it because we don't advertise it in CPUID, but a malicious
         * Guest (or malicious Guest userspace program) could, so we tell the
-         * CPU to disable it before running the Guest. */
+         * CPU to disable it before running the Guest.
+         */
        if (boot_cpu_has(X86_FEATURE_SEP))
                wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);
-        /* Now we actually run the Guest.  It will return when something
+        /*
+         * Now we actually run the Guest.  It will return when something
         * interesting happens, and we can examine its registers to see what it
-         * was doing. */
+         * was doing.
+         */
        run_guest_once(cpu, lguest_pages(raw_smp_processor_id()));
-        /* Note that the "regs" structure contains two extra entries which are
+        /*
+         * Note that the "regs" structure contains two extra entries which are
         * not really registers: a trap number which says what interrupt or
         * trap made the switcher code come back, and an error code which some
-         * traps set.  */
+         * traps set.
+         */
         /* Restore SYSENTER if it's supposed to be on. */
         if (boot_cpu_has(X86_FEATURE_SEP))
                wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
-        /* If the Guest page faulted, then the cr2 register will tell us the
+        /*
+         * If the Guest page faulted, then the cr2 register will tell us the
         * bad virtual address.  We have to grab this now, because once we
         * re-enable interrupts an interrupt could fault and thus overwrite
-         * cr2, or we could even move off to a different CPU. */
+         * cr2, or we could even move off to a different CPU.
+         */
        if (cpu->regs->trapnum == 14)
                cpu->arch.last_pagefault = read_cr2();
-        /* Similarly, if we took a trap because the Guest used the FPU,
+        /*
+         * Similarly, if we took a trap because the Guest used the FPU,
         * we have to restore the FPU it expects to see.
         * math_state_restore() may sleep and we may even move off to
         * a different CPU. So all the critical stuff should be done
-         * before this.  */
+         * before this.
+         */
        else if (cpu->regs->trapnum == 7)
                math_state_restore();
 }
-/*H:130 Now we've examined the hypercall code; our Guest can make requests.
+/*H:130
+ * Now we've examined the hypercall code; our Guest can make requests.
 * Our Guest is usually so well behaved; it never tries to do things it isn't
 * allowed to, and uses hypercalls instead.  Unfortunately, Linux's paravirtual
 * infrastructure isn't quite complete, because it doesn't contain replacements
@@ -225,26 +264,33 @@ void lguest_arch_run_guest(struct lg_cpu *cpu)
 *
 * When the Guest uses one of these instructions, we get a trap (General
 * Protection Fault) and come here.  We see if it's one of those troublesome
- * instructions and skip over it.  We return true if we did. */
+ * instructions and skip over it.  We return true if we did.
+ */
 static int emulate_insn(struct lg_cpu *cpu)
 {
        u8 insn;
        unsigned int insnlen = 0, in = 0, shift = 0;
-        /* The eip contains the *virtual* address of the Guest's instruction:
+        /*
-         * guest_pa just subtracts the Guest's page_offset. */
+         * The eip contains the *virtual* address of the Guest's instruction:
+         * guest_pa just subtracts the Guest's page_offset.
+         */
        unsigned long physaddr = guest_pa(cpu, cpu->regs->eip);
-        /* This must be the Guest kernel trying to do something, not userspace!
+        /*
+         * This must be the Guest kernel trying to do something, not userspace!
         * The bottom two bits of the CS segment register are the privilege
-         * level. */
+         * level.
+         */
        if ((cpu->regs->cs & 3) != GUEST_PL)
                return 0;
        /* Decoding x86 instructions is icky. */
        insn = lgread(cpu, physaddr, u8);
-        /* 0x66 is an "operand prefix".  It means it's using the upper 16 bits
+        /*
-           of the eax register. */
+         * 0x66 is an "operand prefix".  It means it's using the upper 16 bits
+         * of the eax register.
+         */
        if (insn == 0x66) {
                shift = 16;
                /* The instruction is 1 byte so far, read the next byte. */
@@ -252,8 +298,10 @@ static int emulate_insn(struct lg_cpu *cpu)
                insn = lgread(cpu, physaddr + insnlen, u8);
        }
-        /* We can ignore the lower bit for the moment and decode the 4 opcodes
+        /*
-         * we need to emulate. */
+         * We can ignore the lower bit for the moment and decode the 4 opcodes
+         * we need to emulate.
+         */
        switch (insn & 0xFE) {
        case 0xE4: /* in     <next byte>,%al */
                insnlen += 2;
@@ -274,9 +322,11 @@ static int emulate_insn(struct lg_cpu *cpu)
                return 0;
        }
-        /* If it was an "IN" instruction, they expect the result to be read
+        /*
+         * If it was an "IN" instruction, they expect the result to be read
         * into %eax, so we change %eax.  We always return all-ones, which
-         * traditionally means "there's nothing there". */
+         * traditionally means "there's nothing there".
+         */
        if (in) {
                /* Lower bit tells is whether it's a 16 or 32 bit access */
                if (insn & 0x1)
@@ -290,7 +340,8 @@ static int emulate_insn(struct lg_cpu *cpu)
        return 1;
 }
-/* Our hypercalls mechanism used to be based on direct software interrupts.
+/*
+ * Our hypercalls mechanism used to be based on direct software interrupts.
 * After Anthony's "Refactor hypercall infrastructure" kvm patch, we decided to
 * change over to using kvm hypercalls.
 *
@@ -318,16 +369,20 @@ static int emulate_insn(struct lg_cpu *cpu)
 */
 static void rewrite_hypercall(struct lg_cpu *cpu)
 {
-        /* This are the opcodes we use to patch the Guest.  The opcode for "int
+        /*
+         * This are the opcodes we use to patch the Guest.  The opcode for "int
         * $0x1f" is "0xcd 0x1f" but vmcall instruction is 3 bytes long, so we
-         * complete the sequence with a NOP (0x90). */
+         * complete the sequence with a NOP (0x90).
+         */
        u8 insn[3] = {0xcd, 0x1f, 0x90};
        __lgwrite(cpu, guest_pa(cpu, cpu->regs->eip), insn, sizeof(insn));
-        /* The above write might have caused a copy of that page to be made
+        /*
+         * The above write might have caused a copy of that page to be made
         * (if it was read-only).  We need to make sure the Guest has
         * up-to-date pagetables.  As this doesn't happen often, we can just
-         * drop them all. */
+         * drop them all.
+         */
        guest_pagetable_clear_all(cpu);
 }
@@ -335,9 +390,11 @@ static bool is_hypercall(struct lg_cpu *cpu)
 {
        u8 insn[3];
-        /* This must be the Guest kernel trying to do something.
+        /*
+         * This must be the Guest kernel trying to do something.
         * The bottom two bits of the CS segment register are the privilege
-         * level. */
+         * level.
+         */
        if ((cpu->regs->cs & 3) != GUEST_PL)
                return false;
@@ -351,86 +408,105 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu)
 {
        switch (cpu->regs->trapnum) {
        case 13: /* We've intercepted a General Protection Fault. */
-                /* Check if this was one of those annoying IN or OUT
+                /*
+                 * Check if this was one of those annoying IN or OUT
                 * instructions which we need to emulate.  If so, we just go
-                 * back into the Guest after we've done it. */
+                 * back into the Guest after we've done it.
+                 */
                if (cpu->regs->errcode == 0) {
                        if (emulate_insn(cpu))
                                return;
                }
-                /* If KVM is active, the vmcall instruction triggers a
+                /*
-                 * General Protection Fault.  Normally it triggers an
+                 * If KVM is active, the vmcall instruction triggers a General
-                 * invalid opcode fault (6): */
+                 * Protection Fault.  Normally it triggers an invalid opcode
+                 * fault (6):
+                 */
        case 6:
-                /* We need to check if ring == GUEST_PL and
+                /*
-                 * faulting instruction == vmcall. */
+                 * We need to check if ring == GUEST_PL and faulting
+                 * instruction == vmcall.
+                 */
                if (is_hypercall(cpu)) {
                        rewrite_hypercall(cpu);
                        return;
                }
                break;
        case 14: /* We've intercepted a Page Fault. */
-                /* The Guest accessed a virtual address that wasn't mapped.
+                /*
+                 * The Guest accessed a virtual address that wasn't mapped.
                 * This happens a lot: we don't actually set up most of the page
                 * tables for the Guest at all when we start: as it runs it asks
                 * for more and more, and we set them up as required. In this
                 * case, we don't even tell the Guest that the fault happened.
                 *
                 * The errcode tells whether this was a read or a write, and
-                 * whether kernel or userspace code. */
+                 * whether kernel or userspace code.
+                 */
                if (demand_page(cpu, cpu->arch.last_pagefault,
                                cpu->regs->errcode))
                        return;
-                /* OK, it's really not there (or not OK): the Guest needs to
+                /*
+                 * OK, it's really not there (or not OK): the Guest needs to
                 * know.  We write out the cr2 value so it knows where the
                 * fault occurred.
                 *
                 * Note that if the Guest were really messed up, this could
                 * happen before it's done the LHCALL_LGUEST_INIT hypercall, so
-                 * lg->lguest_data could be NULL */
+                 * lg->lguest_data could be NULL
+                 */
                if (cpu->lg->lguest_data &&
                    put_user(cpu->arch.last_pagefault,
                             &cpu->lg->lguest_data->cr2))
                        kill_guest(cpu, "Writing cr2");
                break;
        case 7: /* We've intercepted a Device Not Available fault. */
-                /* If the Guest doesn't want to know, we already restored the
+                /*
-                 * Floating Point Unit, so we just continue without telling
+                 * If the Guest doesn't want to know, we already restored the
-                 * it. */
+                 * Floating Point Unit, so we just continue without telling it.
+                 */
                if (!cpu->ts)
                        return;
                break;
        case 32 ... 255:
-                /* These values mean a real interrupt occurred, in which case
+                /*
+                 * These values mean a real interrupt occurred, in which case
                 * the Host handler has already been run. We just do a
                 * friendly check if another process should now be run, then
-                 * return to run the Guest again */
+                 * return to run the Guest again
+                 */
                cond_resched();
                return;
        case LGUEST_TRAP_ENTRY:
-                /* Our 'struct hcall_args' maps directly over our regs: we set
+                /*
-                 * up the pointer now to indicate a hypercall is pending. */
+                 * Our 'struct hcall_args' maps directly over our regs: we set
+                 * up the pointer now to indicate a hypercall is pending.
+                 */
                cpu->hcall = (struct hcall_args *)cpu->regs;
                return;
        }
        /* We didn't handle the trap, so it needs to go to the Guest. */
        if (!deliver_trap(cpu, cpu->regs->trapnum))
-                /* If the Guest doesn't have a handler (either it hasn't
+                /*
+                 * If the Guest doesn't have a handler (either it hasn't
                 * registered any yet, or it's one of the faults we don't let
-                 * it handle), it dies with this cryptic error message. */
+                 * it handle), it dies with this cryptic error message.
+                 */
                kill_guest(cpu, "unhandled trap %li at %#lx (%#lx)",
                           cpu->regs->trapnum, cpu->regs->eip,
                           cpu->regs->trapnum == 14 ? cpu->arch.last_pagefault
                           : cpu->regs->errcode);
 }
-/* Now we can look at each of the routines this calls, in increasing order of
+/*
+ * Now we can look at each of the routines this calls, in increasing order of
 * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
 * deliver_trap() and demand_page().  After all those, we'll be ready to
 * examine the Switcher, and our philosophical understanding of the Host/Guest
- * duality will be complete. :*/
+ * duality will be complete.
+:*/
 static void adjust_pge(void *on)
 {
        if (on)
@@ -439,13 +515,16 @@ static void adjust_pge(void *on)
                write_cr4(read_cr4() & ~X86_CR4_PGE);
 }
-/*H:020 Now the Switcher is mapped and every thing else is ready, we need to do
+/*H:020
- * some more i386-specific initialization. */
+ * Now the Switcher is mapped and every thing else is ready, we need to do
+ * some more i386-specific initialization.
+ */
 void __init lguest_arch_host_init(void)
 {
        int i;
-        /* Most of the i386/switcher.S doesn't care that it's been moved; on
+        /*
+         * Most of the i386/switcher.S doesn't care that it's been moved; on
         * Intel, jumps are relative, and it doesn't access any references to
         * external code or data.
         *
@@ -453,7 +532,8 @@ void __init lguest_arch_host_init(void)
         * addresses are placed in a table (default_idt_entries), so we need to
         * update the table with the new addresses.  switcher_offset() is a
         * convenience function which returns the distance between the
-         * compiled-in switcher code and the high-mapped copy we just made. */
+         * compiled-in switcher code and the high-mapped copy we just made.
+         */
        for (i = 0; i < IDT_ENTRIES; i++)
                default_idt_entries[i] += switcher_offset();
@@ -468,63 +548,81 @@ void __init lguest_arch_host_init(void)
        for_each_possible_cpu(i) {
                /* lguest_pages() returns this CPU's two pages. */
                struct lguest_pages *pages = lguest_pages(i);
-                /* This is a convenience pointer to make the code fit one
+                /* This is a convenience pointer to make the code neater. */
-                 * statement to a line. */
                struct lguest_ro_state *state = &pages->state;
-                /* The Global Descriptor Table: the Host has a different one
+                /*
+                 * The Global Descriptor Table: the Host has a different one
                 * for each CPU.  We keep a descriptor for the GDT which says
                 * where it is and how big it is (the size is actually the last
-                 * byte, not the size, hence the "-1"). */
+                 * byte, not the size, hence the "-1").
+                 */
                state->host_gdt_desc.size = GDT_SIZE-1;
                state->host_gdt_desc.address = (long)get_cpu_gdt_table(i);
-                /* All CPUs on the Host use the same Interrupt Descriptor
+                /*
+                 * All CPUs on the Host use the same Interrupt Descriptor
                 * Table, so we just use store_idt(), which gets this CPU's IDT
-                 * descriptor. */
+                 * descriptor.
+                 */
                store_idt(&state->host_idt_desc);
-                /* The descriptors for the Guest's GDT and IDT can be filled
+                /*
+                 * The descriptors for the Guest's GDT and IDT can be filled
                 * out now, too.  We copy the GDT & IDT into ->guest_gdt and
-                 * ->guest_idt before actually running the Guest. */
+                 * ->guest_idt before actually running the Guest.
+                 */
                state->guest_idt_desc.size = sizeof(state->guest_idt)-1;
                state->guest_idt_desc.address = (long)&state->guest_idt;
                state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1;
                state->guest_gdt_desc.address = (long)&state->guest_gdt;
-                /* We know where we want the stack to be when the Guest enters
+                /*
+                 * We know where we want the stack to be when the Guest enters
                 * the Switcher: in pages->regs.  The stack grows upwards, so
-                 * we start it at the end of that structure. */
+                 * we start it at the end of that structure.
+                 */
                state->guest_tss.sp0 = (long)(&pages->regs + 1);
-                /* And this is the GDT entry to use for the stack: we keep a
+                /*
-                 * couple of special LGUEST entries. */
+                 * And this is the GDT entry to use for the stack: we keep a
+                 * couple of special LGUEST entries.
+                 */
                state->guest_tss.ss0 = LGUEST_DS;
-                /* x86 can have a finegrained bitmap which indicates what I/O
+                /*
+                 * x86 can have a finegrained bitmap which indicates what I/O
                 * ports the process can use.  We set it to the end of our
-                 * structure, meaning "none". */
+                 * structure, meaning "none".
+                 */
                state->guest_tss.io_bitmap_base = sizeof(state->guest_tss);
-                /* Some GDT entries are the same across all Guests, so we can
+                /*
-                 * set them up now. */
+                 * Some GDT entries are the same across all Guests, so we can
+                 * set them up now.
+                 */
                setup_default_gdt_entries(state);
                /* Most IDT entries are the same for all Guests, too.*/
                setup_default_idt_entries(state, default_idt_entries);
-                /* The Host needs to be able to use the LGUEST segments on this
+                /*
-                 * CPU, too, so put them in the Host GDT. */
+                 * The Host needs to be able to use the LGUEST segments on this
+                 * CPU, too, so put them in the Host GDT.
+                 */
                get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
                get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
        }
-        /* In the Switcher, we want the %cs segment register to use the
+        /*
+         * In the Switcher, we want the %cs segment register to use the
         * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
         * it will be undisturbed when we switch.  To change %cs and jump we
-         * need this structure to feed to Intel's "lcall" instruction. */
+         * need this structure to feed to Intel's "lcall" instruction.
+         */
        lguest_entry.offset = (long)switch_to_guest + switcher_offset();
        lguest_entry.segment = LGUEST_CS;
-        /* Finally, we need to turn off "Page Global Enable".  PGE is an
+        /*
+         * Finally, we need to turn off "Page Global Enable".  PGE is an
         * optimization where page table entries are specially marked to show
         * they never change.  The Host kernel marks all the kernel pages this
         * way because it's always present, even when userspace is running.
@@ -534,16 +632,21 @@ void __init lguest_arch_host_init(void)
         * you'll get really weird bugs that you'll chase for two days.
         *
         * I used to turn PGE off every time we switched to the Guest and back
-         * on when we return, but that slowed the Switcher down noticibly. */
+         * on when we return, but that slowed the Switcher down noticibly.
+         */
-        /* We don't need the complexity of CPUs coming and going while we're
+        /*
-         * doing this. */
+         * We don't need the complexity of CPUs coming and going while we're
+         * doing this.
+         */
        get_online_cpus();
        if (cpu_has_pge) { /* We have a broader idea of "global". */
                /* Remember that this was originally set (for cleanup). */
                cpu_had_pge = 1;
-                /* adjust_pge is a helper function which sets or unsets the PGE
+                /*
-                 * bit on its CPU, depending on the argument (0 == unset). */
+                 * adjust_pge is a helper function which sets or unsets the PGE
+                 * bit on its CPU, depending on the argument (0 == unset).
+                 */
                on_each_cpu(adjust_pge, (void *)0, 1);
                /* Turn off the feature in the global feature set. */
                clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
@@ -590,26 +693,32 @@ int lguest_arch_init_hypercalls(struct lg_cpu *cpu)
 {
        u32 tsc_speed;
-        /* The pointer to the Guest's "struct lguest_data" is the only argument.
+        /*
-         * We check that address now. */
+         * The pointer to the Guest's "struct lguest_data" is the only argument.
+         * We check that address now.
+         */
        if (!lguest_address_ok(cpu->lg, cpu->hcall->arg1,
                               sizeof(*cpu->lg->lguest_data)))
                return -EFAULT;
-        /* Having checked it, we simply set lg->lguest_data to point straight
+        /*
+         * Having checked it, we simply set lg->lguest_data to point straight
         * into the Launcher's memory at the right place and then use
         * copy_to_user/from_user from now on, instead of lgread/write.  I put
         * this in to show that I'm not immune to writing stupid
-         * optimizations. */
+         * optimizations.
+         */
        cpu->lg->lguest_data = cpu->lg->mem_base + cpu->hcall->arg1;
-        /* We insist that the Time Stamp Counter exist and doesn't change with
+        /*
+         * We insist that the Time Stamp Counter exist and doesn't change with
         * cpu frequency.  Some devious chip manufacturers decided that TSC
         * changes could be handled in software.  I decided that time going
         * backwards might be good for benchmarks, but it's bad for users.
         *
         * We also insist that the TSC be stable: the kernel detects unreliable
-         * TSCs for its own purposes, and we use that here. */
+         * TSCs for its own purposes, and we use that here.
+         */
        if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable())
                tsc_speed = tsc_khz;
        else
@@ -625,38 +734,47 @@ int lguest_arch_init_hypercalls(struct lg_cpu *cpu)
 }
 /*:*/
-/*L:030 lguest_arch_setup_regs()
+/*L:030
+ * lguest_arch_setup_regs()
 *
 * Most of the Guest's registers are left alone: we used get_zeroed_page() to
- * allocate the structure, so they will be 0. */
+ * allocate the structure, so they will be 0.
+ */
 void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start)
 {
        struct lguest_regs *regs = cpu->regs;
-        /* There are four "segment" registers which the Guest needs to boot:
+        /*
+         * There are four "segment" registers which the Guest needs to boot:
         * The "code segment" register (cs) refers to the kernel code segment
         * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
         * refer to the kernel data segment __KERNEL_DS.
         *
         * The privilege level is packed into the lower bits.  The Guest runs
-         * at privilege level 1 (GUEST_PL).*/
+         * at privilege level 1 (GUEST_PL).
+         */
        regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
        regs->cs = __KERNEL_CS|GUEST_PL;
-        /* The "eflags" register contains miscellaneous flags.  Bit 1 (0x002)
+        /*
+         * The "eflags" register contains miscellaneous flags.  Bit 1 (0x002)
         * is supposed to always be "1".  Bit 9 (0x200) controls whether
         * interrupts are enabled.  We always leave interrupts enabled while
-         * running the Guest. */
+         * running the Guest.
+         */
        regs->eflags = X86_EFLAGS_IF | 0x2;
-        /* The "Extended Instruction Pointer" register says where the Guest is
+        /*
-         * running. */
+         * The "Extended Instruction Pointer" register says where the Guest is
+         * running.
+         */
        regs->eip = start;
-        /* %esi points to our boot information, at physical address 0, so don't
+        /*
-         * touch it. */
+         * %esi points to our boot information, at physical address 0, so don't
+         * touch it.
+         */
-        /* There are a couple of GDT entries the Guest expects when first
+        /* There are a couple of GDT entries the Guest expects at boot. */
-         * booting. */
        setup_guest_gdt(cpu);
 }
diff --git a/drivers/lguest/x86/switcher_32.S b/drivers/lguest/x86/switcher_32.S
index 3fc15318a80f..40634b0db9f7 100644
--- a/drivers/lguest/x86/switcher_32.S
+++ b/drivers/lguest/x86/switcher_32.S
@@ -1,12 +1,15 @@
-/*P:900 This is the Switcher: code which sits at 0xFFC00000 astride both the
+/*P:900
- * Host and Guest to do the low-level Guest<->Host switch.  It is as simple as
+ * This is the Switcher: code which sits at 0xFFC00000 (or 0xFFE00000) astride
- * it can be made, but it's naturally very specific to x86.
+ * both the Host and Guest to do the low-level Guest<->Host switch.  It is as
+ * simple as it can be made, but it's naturally very specific to x86.
 *
 * You have now completed Preparation.  If this has whet your appetite; if you
 * are feeling invigorated and refreshed then the next, more challenging stage
- * can be found in "make Guest". :*/
+ * can be found in "make Guest".
+ :*/
-/*M:012 Lguest is meant to be simple: my rule of thumb is that 1% more LOC must
+/*M:012
+ * Lguest is meant to be simple: my rule of thumb is that 1% more LOC must
 * gain at least 1% more performance.  Since neither LOC nor performance can be
 * measured beforehand, it generally means implementing a feature then deciding
 * if it's worth it.  And once it's implemented, who can say no?
@@ -31,11 +34,14 @@
 * Host (which is actually really easy).
 *
 * Two questions remain.  Would the performance gain outweigh the complexity?
- * And who would write the verse documenting it? :*/
+ * And who would write the verse documenting it?
+:*/
-/*M:011 Lguest64 handles NMI.  This gave me NMI envy (until I looked at their
+/*M:011
+ * Lguest64 handles NMI.  This gave me NMI envy (until I looked at their
 * code).  It's worth doing though, since it would let us use oprofile in the
- * Host when a Guest is running. :*/
+ * Host when a Guest is running.
+:*/
 /*S:100
 * Welcome to the Switcher itself!