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Subject[PATCH] KVM: X86: fix a bad_page bug_on path
Date
When poweroff L1 Guest with L2 guset on L1, it exists a path to
trigger a bad_page bug_on.
!page_count(pfn_to_page(pfn)) Warning in mmu_spte_clear_track_bits will
appear before,then it may set A/D bit for the freed page and trigger a
bad_page bug_on.

Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
---
arch/x86/kvm/mmu.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index eca30c1..398de96 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -711,12 +711,8 @@ static int mmu_spte_clear_track_bits(u64 *sptep)

pfn = spte_to_pfn(old_spte);

- /*
- * KVM does not hold the refcount of the page used by
- * kvm mmu, before reclaiming the page, we should
- * unmap it from mmu first.
- */
- WARN_ON(!kvm_is_reserved_pfn(pfn) && !page_count(pfn_to_page(pfn)));
+ if (!page_count(pfn_to_page(pfn)))
+ return 1;

if (is_accessed_spte(old_spte))
kvm_set_pfn_accessed(pfn);
--
1.8.3.1
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