Add a WARN_ON_ONCE() sanity check to verify that a nested PML Full VM-Exit is only synthesized when the original VM-Exit from L2 was an EPT Violation. While KVM can fallthrough to kvm_mmu_do_page_fault() if an EPT Misconfig occurs on a stale MMIO SPTE, KVM should not treat the access as a write (there isn't enough information to know *what* the access was), i.e. KVM should never try to insert a PML entry in that case. Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/nested.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 4d0561136e70..29df186dac84 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -416,6 +416,16 @@ static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu, vm_exit_reason = EXIT_REASON_PML_FULL; vmx->nested.pml_full = false; + /* + * It should be impossible to trigger a nested PML Full VM-Exit + * for anything other than an EPT Violation from L2. KVM *can* + * trigger nEPT page fault injection in response to an EPT + * Misconfig, e.g. if the MMIO SPTE was stale and L1's EPT + * tables also changed, but KVM should not treat EPT Misconfig + * VM-Exits as writes. + */ + WARN_ON_ONCE(vmx->exit_reason.basic != EXIT_REASON_EPT_VIOLATION); + /* * PML Full and EPT Violation VM-Exits both use bit 12 to report * "NMI unblocking due to IRET", i.e. the bit can be propagated -- 2.43.0.687.g38aa6559b0-goog
