Linux Virtualization - Mar 2009 - [PATCH 2/5] lguest: wire up pte_update/pte_update_defer

Impact: intermittent guest segv/crash fix

I've been seeing random guest bad address crashes and segmentation faults:
bisect led to 4f98a2fee8 (vmscan: split LRU lists into anon & file sets),
but that's a red herring.

It turns out that lguest never hooked up the pte_update/pte_update_defer
calls, so our ptes were not always in sync.  After the vmscan commit, the
bug became reproducible; now a fsck in a 64MB guest causes reproducible
pagetable corruption.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Cc: jeremy at xensource.com
Cc: virtualization at lists.osdl.org
Cc: stable at kernel.org
---
 arch/x86/lguest/boot.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
index 65f0b8a..c3bdf0b 100644
--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -475,11 +480,17 @@ static void lguest_write_cr4(unsigned long val)
  * into a process' address space.  We set the entry then tell the Host the
  * toplevel and address this corresponds to.  The Guest uses one pagetable per
  * process, so we need to tell the Host which one we're changing
(mm->pgd). */
+static void lguest_pte_update(struct mm_struct *mm, unsigned long addr,
+			       pte_t *ptep)
+{
+	lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low);
+}
+
 static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t pteval)
 {
 	*ptep = pteval;
-	lazy_hcall(LHCALL_SET_PTE, __pa(mm->pgd), addr, pteval.pte_low);
+	lguest_pte_update(mm, addr, ptep);
 }
 
 /* The Guest calls this to set a top-level entry.  Again, we set the entry then
@@ -1018,6 +1046,8 @@ __init void lguest_init(void)
 	pv_mmu_ops.read_cr3 = lguest_read_cr3;
 	pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu;
 	pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
+	pv_mmu_ops.pte_update = lguest_pte_update;
+	pv_mmu_ops.pte_update_defer = lguest_pte_update;
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	/* apic read/write intercepts */