[PATCH 1/4] KVM: fix race condition in kvm_mmu_slot_remove_write_access()

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Suggested by Avi.

Dropping PT_WRITABLE_MASK is under race condition with the hardware.
Use update_spte() to avoid this.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
---
 arch/x86/kvm/mmu.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index bdb9fa9..e716def 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3449,7 +3449,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
 		for (i = 0; i < PT64_ENT_PER_PAGE; ++i)
 			/* avoid RMW */
 			if (is_writable_pte(pt[i]))
-				pt[i] &= ~PT_WRITABLE_MASK;
+				update_spte(&pt[i], pt[i] & ~PT_WRITABLE_MASK);
 	}
 	kvm_flush_remote_tlbs(kvm);
 }
-- 
1.7.1

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