[PATCH 07/16] KVM: x86: Move synthetic PFERR_* sanity checks to SVM's #NPF handler

[Sean Christopherson <seanjc@google.com>]

Move the sanity check that hardware never sets bits that collide with KVM-
define synthetic bits from kvm_mmu_page_fault() to npf_interception(),
i.e. make the sanity check #NPF specific.  The legacy #PF path already
WARNs if _any_ of bits 63:32 are set, and the error code that comes from
VMX's EPT Violatation and Misconfig is 100% synthesized (KVM morphs VMX's
EXIT_QUALIFICATION into error code flags).

Add a compile-time assert in the legacy #PF handler to make sure that KVM-
define flags are covered by its existing sanity check on the upper bits.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 12 +++---------
 arch/x86/kvm/svm/svm.c |  9 +++++++++
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 5d892bd59c97..bd342ebd0809 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4561,6 +4561,9 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
 	if (WARN_ON_ONCE(error_code >> 32))
 		error_code = lower_32_bits(error_code);
 
+	/* Ensure the above sanity check also covers KVM-defined flags. */
+	BUILD_BUG_ON(lower_32_bits(PFERR_SYNTHETIC_MASK));
+
 	vcpu->arch.l1tf_flush_l1d = true;
 	if (!flags) {
 		trace_kvm_page_fault(vcpu, fault_address, error_code);
@@ -5845,15 +5848,6 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 	int r, emulation_type = EMULTYPE_PF;
 	bool direct = vcpu->arch.mmu->root_role.direct;
 
-	/*
-	 * WARN if hardware generates a fault with an error code that collides
-	 * with KVM-defined sythentic flags.  Clear the flags and continue on,
-	 * i.e. don't terminate the VM, as KVM can't possibly be relying on a
-	 * flag that KVM doesn't know about.
-	 */
-	if (WARN_ON_ONCE(error_code & PFERR_SYNTHETIC_MASK))
-		error_code &= ~PFERR_SYNTHETIC_MASK;
-
 	if (WARN_ON_ONCE(!VALID_PAGE(vcpu->arch.mmu->root.hpa)))
 		return RET_PF_RETRY;
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e90b429c84f1..199c4dd8d214 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2055,6 +2055,15 @@ static int npf_interception(struct kvm_vcpu *vcpu)
 	u64 fault_address = svm->vmcb->control.exit_info_2;
 	u64 error_code = svm->vmcb->control.exit_info_1;
 
+	/*
+	 * WARN if hardware generates a fault with an error code that collides
+	 * with KVM-defined sythentic flags.  Clear the flags and continue on,
+	 * i.e. don't terminate the VM, as KVM can't possibly be relying on a
+	 * flag that KVM doesn't know about.
+	 */
+	if (WARN_ON_ONCE(error_code & PFERR_SYNTHETIC_MASK))
+		error_code &= ~PFERR_SYNTHETIC_MASK;
+
 	trace_kvm_page_fault(vcpu, fault_address, error_code);
 	return kvm_mmu_page_fault(vcpu, fault_address, error_code,
 			static_cpu_has(X86_FEATURE_DECODEASSISTS) ?
-- 
2.44.0.278.ge034bb2e1d-goog