lguest: extract shadow PTE walking / allocating.
We want a separate find_pte() function so we can call it for populating the
switcher PTE entries.
We can also use it in page_writable().
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
index f074f34..009c717 100644
--- a/drivers/lguest/page_tables.c
+++ b/drivers/lguest/page_tables.c
@@ -291,6 +291,88 @@
}
#endif
+/*H:331
+ * This is the core routine to walk the shadow page tables and find the page
+ * table entry for a specific address.
+ *
+ * If allocate is set, then we allocate any missing levels, setting the flags
+ * on the new page directory and mid-level directories using the arguments
+ * (which are copied from the Guest's page table entries).
+ */
+static pte_t *find_spte(struct lg_cpu *cpu, unsigned long vaddr, bool allocate,
+ int pgd_flags, int pmd_flags)
+{
+ pgd_t *spgd;
+ /* Mid level for PAE. */
+#ifdef CONFIG_X86_PAE
+ pmd_t *spmd;
+#endif
+
+ /* Get top level entry. */
+ spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
+ if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) {
+ /* No shadow entry: allocate a new shadow PTE page. */
+ unsigned long ptepage;
+
+ /* If they didn't want us to allocate anything, stop. */
+ if (!allocate)
+ return NULL;
+
+ ptepage = get_zeroed_page(GFP_KERNEL);
+ /*
+ * 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 NULL;
+ }
+ /*
+ * 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));
+ }
+
+ /*
+ * Intel's Physical Address Extension actually uses three levels of
+ * page tables, so we need to look in the mid-level.
+ */
+#ifdef CONFIG_X86_PAE
+ /* Now look at the mid-level shadow entry. */
+ spmd = spmd_addr(cpu, *spgd, vaddr);
+
+ if (!(pmd_flags(*spmd) & _PAGE_PRESENT)) {
+ /* No shadow entry: allocate a new shadow PTE page. */
+ unsigned long ptepage;
+
+ /* If they didn't want us to allocate anything, stop. */
+ if (!allocate)
+ return NULL;
+
+ ptepage = get_zeroed_page(GFP_KERNEL);
+
+ /*
+ * 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 pmd page");
+ return NULL;
+ }
+
+ /*
+ * And we copy the flags to the shadow PMD entry. The page
+ * number in the shadow PMD is the page we just allocated.
+ */
+ set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags));
+ }
+#endif
+
+ /* Get the pointer to the shadow PTE entry we're going to set. */
+ return spte_addr(cpu, *spgd, vaddr);
+}
+
/*H:330
* (i) Looking up a page table entry when the Guest faults.
*
@@ -304,17 +386,11 @@
*/
bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
{
- pgd_t gpgd;
- pgd_t *spgd;
unsigned long gpte_ptr;
pte_t gpte;
pte_t *spte;
-
- /* Mid level for PAE. */
-#ifdef CONFIG_X86_PAE
- pmd_t *spmd;
pmd_t gpmd;
-#endif
+ pgd_t gpgd;
/* We never demand page the Switcher, so trying is a mistake. */
if (vaddr >= switcher_addr)
@@ -329,67 +405,31 @@
/* Toplevel not present? We can't map it in. */
if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
return false;
- }
- /* Now look at the matching shadow entry. */
- spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
- 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 kills the Guest if it has weird flags or tries to
+ * refer to a "physical" address outside the bounds.
*/
- if (!ptepage) {
- kill_guest(cpu, "out of memory allocating pte page");
- return false;
- }
- /* We check that the Guest pgd is OK. */
if (!check_gpgd(cpu, gpgd))
return false;
- /*
- * 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)));
}
+ /* This "mid-level" entry is only used for non-linear, PAE mode. */
+ gpmd = __pmd(_PAGE_TABLE);
+
#ifdef CONFIG_X86_PAE
- if (unlikely(cpu->linear_pages)) {
- /* Faking up a linear mapping. */
- gpmd = __pmd(_PAGE_TABLE);
- } else {
+ if (likely(!cpu->linear_pages)) {
gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
/* Middle level not present? We can't map it in. */
if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
return false;
- }
- /* Now look at the matching shadow entry. */
- spmd = spmd_addr(cpu, *spgd, vaddr);
-
- if (!(pmd_flags(*spmd) & _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 kills the Guest if it has weird flags or tries to
+ * refer to a "physical" address outside the bounds.
*/
- if (!ptepage) {
- kill_guest(cpu, "out of memory allocating pte page");
- return false;
- }
-
- /* We check that the Guest pmd is OK. */
if (!check_gpmd(cpu, gpmd))
return false;
-
- /*
- * And we copy the flags to the shadow PMD entry. The page
- * number in the shadow PMD is the page we just allocated.
- */
- set_pmd(spmd, __pmd(__pa(ptepage) | pmd_flags(gpmd)));
}
/*
@@ -441,7 +481,9 @@
gpte = pte_mkdirty(gpte);
/* Get the pointer to the shadow PTE entry we're going to set. */
- spte = spte_addr(cpu, *spgd, vaddr);
+ spte = find_spte(cpu, vaddr, true, pgd_flags(gpgd), pmd_flags(gpmd));
+ if (!spte)
+ return false;
/*
* If there was a valid shadow PTE entry here before, we release it.
@@ -493,33 +535,23 @@
*/
static bool page_writable(struct lg_cpu *cpu, unsigned long vaddr)
{
- pgd_t *spgd;
+ pte_t *spte;
unsigned long flags;
-#ifdef CONFIG_X86_PAE
- pmd_t *spmd;
-#endif
/* You can't put your stack in the Switcher! */
if (vaddr >= switcher_addr)
return false;
- /* Look at the current top level entry: is it present? */
- spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
- if (!(pgd_flags(*spgd) & _PAGE_PRESENT))
+ /* If there's no shadow PTE, it's not writable. */
+ spte = find_spte(cpu, vaddr, false, 0, 0);
+ if (!spte)
return false;
-#ifdef CONFIG_X86_PAE
- spmd = spmd_addr(cpu, *spgd, vaddr);
- if (!(pmd_flags(*spmd) & _PAGE_PRESENT))
- return false;
-#endif
-
/*
* Check the flags on the pte entry itself: it must be present and
* writable.
*/
- flags = pte_flags(*(spte_addr(cpu, *spgd, vaddr)));
-
+ flags = pte_flags(*spte);
return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW);
}