KVM: x86/mmu: Bail early from final #PF handling on spurious faults
Detect spurious page faults, e.g. page faults that occur when multiple vCPUs simultaneously access a not-present page, and skip the SPTE write, prefetch, and stats update for spurious faults. Note, the performance benefits of skipping the write and prefetch are likely negligible, and the false positive stats adjustment is probably lost in the noise. The primary motivation is to play nice with TDX's SEPT in the long term. SEAMCALLs (to program SEPT entries) are quite costly, e.g. thousands of cycles, and a spurious SEPT update will result in a SEAMCALL error (which KVM will ideally treat as fatal). Reported-by: Kai Huang <kai.huang@intel.com> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Message-Id: <20200923220425.18402-5-sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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