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Subject[patch 42/45] lguest: wire up pte_update/pte_update_defer
-stable review patch.  If anyone has any objections, please let us know.

From: Rusty Russell <>

upstream commit: b7ff99ea53cd16de8f6166c0e98f19a7c6ca67ee

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 <>
Signed-off-by: Chris Wright <>
arch/x86/lguest/boot.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

--- a/arch/x86/lguest/boot.c
+++ b/arch/x86/lguest/boot.c
@@ -485,11 +485,17 @@ static void lguest_write_cr4(unsigned lo
* 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
@@ -1034,6 +1040,8 @@ __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;

/* apic read/write intercepts */

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