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KVM: x86/mmu: Bail from fast_page_fault() if SPTE is not shadow-present

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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>
This commit is contained in:
Sean Christopherson
2021-02-25 12:47:28 -08:00
committed by Paolo Bonzini
parent 64bb2769d7
commit ec89e64386
1 changed files with 3 additions and 0 deletions
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3
arch/x86/kvm/mmu/mmu.c
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@@ -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;