Boot with virtual == physical to get closer to native Linux.

1) This allows us to get alot closer to booting bzImages.

2) It means we don't have to know page_offset.

3) The Guest needs to modify the boot pagetables to create the
   PAGE_OFFSET mapping before jumping to C code.

4) guest_pa() walks the page tables rather than using page_offset.

5) We don't use page_offset to figure out whether to emulate: it was
   always kinda quesationable, and won't work for instructions done
   before remapping (bzImage unpacking in particular).

6) We still want the kernel address for tlb flushing: have the initial
   hypercall give us that, too.

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

1 files changed, 40 insertions, 7 deletions

diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index bfe3650b28d6..fe3c7575647b 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -13,6 +13,7 @@
 #include <linux/random.h>
 #include <linux/percpu.h>
 #include <asm/tlbflush.h>
+#include <asm/uaccess.h>
 #include "lg.h"
 
 /*M:008 We hold reference to pages, which prevents them from being swapped.
@@ -345,7 +346,7 @@ static void flush_user_mappings(struct lguest *lg, int idx)
 {
         unsigned int i;
         /* Release every pgd entry up to the kernel's address. */
-        for (i = 0; i < pgd_index(lg->page_offset); i++)
+        for (i = 0; i < pgd_index(lg->kernel_address); i++)
                 release_pgd(lg, lg->pgdirs[idx].pgdir + i);
 }
 
@@ -358,6 +359,25 @@ void guest_pagetable_flush_user(struct lguest *lg)
 }
 /*:*/
 
+/* We walk down the guest page tables to get a guest-physical address */
+unsigned long guest_pa(struct lguest *lg, unsigned long vaddr)
+{
+        pgd_t gpgd;
+        pte_t gpte;
+
+        /* First step: get the top-level Guest page table entry. */
+        gpgd = __pgd(lgread_u32(lg, gpgd_addr(lg, vaddr)));
+        /* Toplevel not present?  We can't map it in. */
+        if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
+                kill_guest(lg, "Bad address %#lx", vaddr);
+
+        gpte = __pte(lgread_u32(lg, gpte_addr(lg, gpgd, vaddr)));
+        if (!(pte_flags(gpte) & _PAGE_PRESENT))
+                kill_guest(lg, "Bad address %#lx", vaddr);
+
+        return pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK);
+}
+
 /* 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. */
@@ -500,7 +520,7 @@ void guest_set_pte(struct lguest *lg,
 {
         /* Kernel mappings must be changed on all top levels.  Slow, but
          * doesn't happen often. */
-        if (vaddr >= lg->page_offset) {
+        if (vaddr >= lg->kernel_address) {
                 unsigned int i;
                 for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++)
                         if (lg->pgdirs[i].pgdir)
@@ -550,11 +570,6 @@ void guest_set_pmd(struct lguest *lg, unsigned long gpgdir, u32 idx)
  * its first page table is.  We set some things up here: */
 int init_guest_pagetable(struct lguest *lg, unsigned long pgtable)
 {
-        /* In flush_user_mappings() we loop from 0 to
-         * "pgd_index(lg->page_offset)".  This assumes it won't hit
-         * the Switcher mappings, so check that now. */
-        if (pgd_index(lg->page_offset) >= SWITCHER_PGD_INDEX)
-                return -EINVAL;
         /* We start on the first shadow page table, and give it a blank PGD
          * page. */
         lg->pgdidx = 0;
@@ -565,6 +580,24 @@ int init_guest_pagetable(struct lguest *lg, unsigned long pgtable)
         return 0;
 }
 
+/* When the Guest calls LHCALL_LGUEST_INIT we do more setup. */
+void page_table_guest_data_init(struct lguest *lg)
+{
+        /* We get the kernel address: above this is all kernel memory. */
+        if (get_user(lg->kernel_address, &lg->lguest_data->kernel_address)
+            /* We tell the Guest that it can't use the top 4MB of virtual
+             * addresses used by the Switcher. */
+            || put_user(4U*1024*1024, &lg->lguest_data->reserve_mem)
+            || put_user(lg->pgdirs[lg->pgdidx].gpgdir,&lg->lguest_data->pgdir))
+                kill_guest(lg, "bad guest page %p", lg->lguest_data);
+
+        /* 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. */
+        if (pgd_index(lg->kernel_address) >= SWITCHER_PGD_INDEX)
+                kill_guest(lg, "bad kernel address %#lx", lg->kernel_address);
+}
+
 /* When a Guest dies, our cleanup is fairly simple. */
 void free_guest_pagetable(struct lguest *lg)
 {