lguest: improve interrupt handling, speed up stream networking

lguest never checked for pending interrupts when enabling interrupts, and
things still worked.  However, it makes a significant difference to TCP
performance, so it's time we fixed it by introducing a pending_irq flag
and checking it on irq_restore and irq_enable.

These two routines are now too big to patch into the 8/10 bytes
patch space, so we drop that code.

Note: The high latency on interrupt delivery had a very curious
effect: once everything else was optimized, networking without GSO was
faster than networking with GSO, since more interrupts were sent and
hence a greater chance of one getting through to the Guest!

Note2: (Almost) Closing the same loophole for iret doesn't have any
measurable effect, so I'm leaving that patch for the moment.

Before:
	1GB tcpblast Guest->Host:		30.7 seconds
	1GB tcpblast Guest->Host (no GSO):	76.0 seconds

After:
	1GB tcpblast Guest->Host:		6.8 seconds
	1GB tcpblast Guest->Host (no GSO):	27.8 seconds

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

8 files changed, 43 insertions, 16 deletions

diff --git a/arch/x86/include/asm/lguest_hcall.h b/arch/x86/include/asm/lguest_hcall.h
index faae1996487b..f9a9f7811248 100644
--- a/arch/x86/include/asm/lguest_hcall.h
+++ b/arch/x86/include/asm/lguest_hcall.h
@@ -17,6 +17,7 @@
 #define LHCALL_LOAD_TLS         16
 #define LHCALL_NOTIFY           17
 #define LHCALL_LOAD_GDT_ENTRY   18
+#define LHCALL_SEND_INTERRUPTS  19
 
 #define LGUEST_TRAP_ENTRY 0x1F
 
diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 2392a7a171c2..37b8c1d3e022 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -205,6 +205,12 @@ PV_CALLEE_SAVE_REGS_THUNK(save_fl);
 static void restore_fl(unsigned long flags)
 {
         lguest_data.irq_enabled = flags;
+        mb();
+        /* Null hcall forces interrupt delivery now, if irq_pending is
+         * set to X86_EFLAGS_IF (ie. an interrupt is pending, and flags
+         * enables interrupts. */
+        if (flags & lguest_data.irq_pending)
+                kvm_hypercall0(LHCALL_SEND_INTERRUPTS);
 }
 PV_CALLEE_SAVE_REGS_THUNK(restore_fl);
 
@@ -219,6 +225,11 @@ PV_CALLEE_SAVE_REGS_THUNK(irq_disable);
 static void irq_enable(void)
 {
         lguest_data.irq_enabled = X86_EFLAGS_IF;
+        mb();
+        /* Null hcall forces interrupt delivery now. */
+        if (lguest_data.irq_pending)
+                kvm_hypercall0(LHCALL_SEND_INTERRUPTS);
+
 }
 PV_CALLEE_SAVE_REGS_THUNK(irq_enable);
 
@@ -972,10 +983,10 @@ static void lguest_restart(char *reason)
  *
  * Our current solution is to allow the paravirt back end to optionally patch
  * over the indirect calls to replace them with something more efficient.  We
- * patch the four most commonly called functions: disable interrupts, enable
- * interrupts, restore interrupts and save interrupts.  We usually have 6 or 10
- * bytes to patch into: the Guest versions of these operations are small enough
- * that we can fit comfortably.
+ * patch two of the simplest of the most commonly called functions: disable
+ * interrupts and save interrupts.  We usually have 6 or 10 bytes to patch
+ * into: the Guest versions of these operations are small enough that we can
+ * fit comfortably.
  *
  * First we need assembly templates of each of the patchable Guest operations,
  * and these are in i386_head.S. */
@@ -986,8 +997,6 @@ static const struct lguest_insns
         const char *start, *end;
 } lguest_insns[] = {
         [PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli },
-        [PARAVIRT_PATCH(pv_irq_ops.irq_enable)] = { lgstart_sti, lgend_sti },
-        [PARAVIRT_PATCH(pv_irq_ops.restore_fl)] = { lgstart_popf, lgend_popf },
         [PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf },
 };
 
diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S
index f79541989471..3e0c5545d59c 100644
--- a/arch/x86/lguest/i386_head.S
+++ b/arch/x86/lguest/i386_head.S
@@ -46,8 +46,6 @@ ENTRY(lguest_entry)
         .globl lgstart_##name; .globl lgend_##name
 
 LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(sti, movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled)
-LGUEST_PATCH(popf, movl %eax, lguest_data+LGUEST_DATA_irq_enabled)
 LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
 /*:*/
 
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c
index 8ca1def5b142..03fbc88c0023 100644
--- a/drivers/lguest/core.c
+++ b/drivers/lguest/core.c
@@ -189,6 +189,7 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
         /* We stop running once the Guest is dead. */
         while (!cpu->lg->dead) {
                 unsigned int irq;
+                bool more;
 
                 /* First we run any hypercalls the Guest wants done. */
                 if (cpu->hcall)
@@ -213,9 +214,9 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                 /* 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. */
-                irq = interrupt_pending(cpu);
+                irq = interrupt_pending(cpu, &more);
                 if (irq < LGUEST_IRQS)
-                        try_deliver_interrupt(cpu, irq);
+                        try_deliver_interrupt(cpu, irq, more);
 
                 /* All long-lived kernel loops need to check with this horrible
                  * thing called the freezer.  If the Host is trying to suspend,
@@ -233,7 +234,7 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
                         set_current_state(TASK_INTERRUPTIBLE);
                         /* Just before we sleep, make sure nothing snuck in
                          * which we should be doing. */
-                        if (interrupt_pending(cpu) < LGUEST_IRQS
+                        if (interrupt_pending(cpu, &more) < LGUEST_IRQS
                             || cpu->break_out)
                                 set_current_state(TASK_RUNNING);
                         else
diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
index 54d66f05fefa..f252b71ae79e 100644
--- a/drivers/lguest/hypercalls.c
+++ b/drivers/lguest/hypercalls.c
@@ -37,6 +37,10 @@ static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
                 /* 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. */
+                break;
         case LHCALL_LGUEST_INIT:
                 /* You can't get here unless you're already initialized.  Don't
                  * do that. */
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c
index a8c966fee1e4..5a10754b4790 100644
--- a/drivers/lguest/interrupts_and_traps.c
+++ b/drivers/lguest/interrupts_and_traps.c
@@ -131,7 +131,7 @@ 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. */
-unsigned int interrupt_pending(struct lg_cpu *cpu)
+unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
 {
         unsigned int irq;
         DECLARE_BITMAP(blk, LGUEST_IRQS);
@@ -149,13 +149,14 @@ unsigned int interrupt_pending(struct lg_cpu *cpu)
 
         /* Find the first interrupt. */
         irq = find_first_bit(blk, LGUEST_IRQS);
+        *more = find_next_bit(blk, LGUEST_IRQS, irq+1);
 
         return irq;
 }
 
 /* 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)
+void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
 {
         struct desc_struct *idt;
 
@@ -178,8 +179,12 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq)
                 u32 irq_enabled;
                 if (get_user(irq_enabled, &cpu->lg->lguest_data->irq_enabled))
                         irq_enabled = 0;
-                if (!irq_enabled)
+                if (!irq_enabled) {
+                        /* Make sure they know an IRQ is pending. */
+                        put_user(X86_EFLAGS_IF,
+                                 &cpu->lg->lguest_data->irq_pending);
                         return;
+                }
         }
 
         /* Look at the IDT entry the Guest gave us for this interrupt.  The
@@ -202,6 +207,11 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq)
          * here is a compromise which means at least it gets updated every
          * timer interrupt. */
         write_timestamp(cpu);
+
+        /* 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);
 }
 /*:*/
 
diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
index 6743cf147d97..573896533ac9 100644
--- a/drivers/lguest/lg.h
+++ b/drivers/lguest/lg.h
@@ -139,8 +139,8 @@ int run_guest(struct lg_cpu *cpu, unsigned long __user *user);
 #define pgd_pfn(x)      (pgd_val(x) >> PAGE_SHIFT)
 
 /* interrupts_and_traps.c: */
-unsigned int interrupt_pending(struct lg_cpu *cpu);
-void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq);
+unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more);
+void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more);
 bool deliver_trap(struct lg_cpu *cpu, unsigned int num);
 void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int i,
                           u32 low, u32 hi);
diff --git a/include/linux/lguest.h b/include/linux/lguest.h
index 175e63f4a8c0..7bc1440fc473 100644
--- a/include/linux/lguest.h
+++ b/include/linux/lguest.h
@@ -30,6 +30,10 @@ struct lguest_data
         /* Wallclock time set by the Host. */
         struct timespec time;
 
+        /* Interrupt pending set by the Host.  The Guest should do a hypercall
+         * if it re-enables interrupts and sees this set (to X86_EFLAGS_IF). */
+        int irq_pending;
+
         /* Async hypercall ring.  Instead of directly making hypercalls, we can
          * place them in here for processing the next time the Host wants.
          * This batching can be quite efficient. */