From ec89e643867148ab4a2a856a38717d2e89692be7 Mon Sep 17 00:00:00 2001 From: Sean Christopherson <seanjc@google.com> Date: Thu, 25 Feb 2021 12:47:28 -0800 Subject: [PATCH] KVM: x86/mmu: Bail from fast_page_fault() if SPTE is not shadow-present Bail from fast_page_fault() if the SPTE is not a shadow-present SPTE. Functionally, this is not strictly necessary as the !is_access_allowed() check will eventually reject the fast path, but an early check on shadow-present skips unnecessary checks and will allow a future patch to tweak the A/D status auditing to warn if KVM attempts to query A/D bits without first ensuring the SPTE is a shadow-present SPTE. Note, is_shadow_present_pte() is quite expensive at this time, i.e. this might be a net negative in the short term. A future patch will optimize is_shadow_present_pte() to a single AND operation and remedy the issue. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20210225204749.1512652-4-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- arch/x86/kvm/mmu/mmu.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index cfa8265b321e8..474c2b6dbc9e7 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3063,6 +3063,9 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, if (!is_shadow_present_pte(spte)) break; + if (!is_shadow_present_pte(spte)) + break; + sp = sptep_to_sp(iterator.sptep); if (!is_last_spte(spte, sp->role.level)) break; -- GitLab