KVM: x86/mmu: Don't save mmu_invalidate_seq after checking private attr

Drop the second snapshot of mmu_invalidate_seq in kvm_faultin_pfn().
Before checking the mismatch of private vs. shared, mmu_invalidate_seq is
saved to fault->mmu_seq, which can be used to detect an invalidation
related to the gfn occurred, i.e. KVM will not install a mapping in page
table if fault->mmu_seq != mmu_invalidate_seq.

Currently there is a second snapshot of mmu_invalidate_seq, which may not
be same as the first snapshot in kvm_faultin_pfn(), i.e. the gfn attribute
may be changed between the two snapshots, but the gfn may be mapped in
page table without hindrance. Therefore, drop the second snapshot as it
has no obvious benefits.

Fixes: f6adeae81f35 ("KVM: x86/mmu: Handle no-slot faults at the beginning of kvm_faultin_pfn()")
Signed-off-by: Tao Su <tao1.su@linux.intel.com>
Message-ID: <20240528102234.2162763-1-tao1.su@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b7b4426..8d74bde 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4411,9 +4411,6 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
                        return RET_PF_EMULATE;
        }
 
-       fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq;
-       smp_rmb();
-
        /*
         * Check for a relevant mmu_notifier invalidation event before getting
         * the pfn from the primary MMU, and before acquiring mmu_lock.