diff options
| author | Sean Christopherson <seanjc@google.com> | 2022-04-23 03:47:45 +0000 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-05-12 09:51:41 -0400 |
| commit | 5c64aba5179f6fc6a367f76342c6290a5e06cfc4 (patch) | |
| tree | c007219802a412883eb51974198d4dd63d6c6b8c /arch/x86/kvm | |
| parent | 54275f74cf384217d9e6e85629793f0a024d88b7 (diff) | |
| download | linux-5c64aba5179f6fc6a367f76342c6290a5e06cfc4.tar.bz2 | |
KVM: x86/mmu: Drop exec/NX check from "page fault can be fast"
Tweak the "page fault can be fast" logic to explicitly check for !PRESENT
faults in the access tracking case, and drop the exec/NX check that
becomes redundant as a result. No sane hardware will generate an access
that is both an instruct fetch and a write, i.e. it's a waste of cycles.
If hardware goes off the rails, or KVM runs under a misguided hypervisor,
spuriously running throught fast path is benign (KVM has been uknowingly
being doing exactly that for years).
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220423034752.1161007-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/mmu/mmu.c | 19 |
1 files changed, 12 insertions, 7 deletions
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index f36e3cdde25d..add486220dae 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3044,16 +3044,14 @@ static bool handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fa static bool page_fault_can_be_fast(struct kvm_page_fault *fault) { /* - * Do not fix the mmio spte with invalid generation number which - * need to be updated by slow page fault path. + * Page faults with reserved bits set, i.e. faults on MMIO SPTEs, only + * reach the common page fault handler if the SPTE has an invalid MMIO + * generation number. Refreshing the MMIO generation needs to go down + * the slow path. Note, EPT Misconfigs do NOT set the PRESENT flag! */ if (fault->rsvd) return false; - /* See if the page fault is due to an NX violation */ - if (unlikely(fault->exec && fault->present)) - return false; - /* * #PF can be fast if: * @@ -3069,7 +3067,14 @@ static bool page_fault_can_be_fast(struct kvm_page_fault *fault) * SPTE is MMU-writable (determined later), the fault can be fixed * by setting the Writable bit, which can be done out of mmu_lock. */ - return !kvm_ad_enabled() || (fault->write && fault->present); + if (!fault->present) + return !kvm_ad_enabled(); + + /* + * Note, instruction fetches and writes are mutually exclusive, ignore + * the "exec" flag. + */ + return fault->write; } /* |