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Message-ID: <20240209221700.393189-4-seanjc@google.com>
Date: Fri, 9 Feb 2024 14:17:00 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] KVM: nVMX: Add a sanity check that nested PML Full stems
from EPT Violations
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@...gle.com>
---
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
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