From: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
This can happen in the following scenario:
vcpu0 vcpu1
read fault
gup(.write=0)
gup(.write=1)
reuse swap cache, no COW
set writable spte
use writable spte
set read-only spte
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 4787035..7ae2712 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2069,6 +2069,16 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
spte_to_pfn(*sptep), pfn);
drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
kvm_flush_remote_tlbs(vcpu->kvm);
+ /*
+ * If we overwrite a writable spte with a read-only one,
+ * drop it and flush remote TLBs. Otherwise rmap_write_protect
+ * will find a read-only spte, even though the writable spte
+ * might be cached on a CPU's TLB.
+ */
+ } else if (is_writable_pte(*sptep) &&
+ (!(pte_access & ACC_WRITE_MASK) || !dirty)) {
+ drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
+ kvm_flush_remote_tlbs(vcpu->kvm);
} else
was_rmapped = 1;
}
--
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