[PATCH 21/22] KVM: SVM: work around errata 1218

[Paolo Bonzini]

According to AMD, the hypervisor may not be able to determine whether a
fault was a GMET fault or an NX fault based on EXITINFO1, and software
"must read the relevant VMCB to determine whether a fault was a GMET
fault or an NX fault".  The APM further details that they meant the
CPL field.

KVM uses the page fault error code to distinguish the causes of a
nested page fault, so recalculate the PFERR_USER_MASK bit of the
vmexit information.  Only do it for fetches and only if GMET is in
use, because KVM does not differentiate based on PFERR_USER_MASK
for other nested NPT page faults.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/svm/svm.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 4a4f663b2bd2..d3b69eb3242b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1955,6 +1955,17 @@ static int npf_interception(struct kvm_vcpu *vcpu)
 	if (WARN_ON_ONCE(error_code & PFERR_SYNTHETIC_MASK))
 		error_code &= ~PFERR_SYNTHETIC_MASK;
 
+	if ((svm->vmcb->control.nested_ctl & SVM_NESTED_CTL_GMET_ENABLE) &&
+	    (error_code & PFERR_FETCH_MASK)) {
+		/*
+		 * Work around errata 1218: EXITINFO1[2] May Be Incorrectly Set
+		 * When GMET (Guest Mode Execute Trap extension) is Enabled
+		 */
+		error_code |= PFERR_USER_MASK;
+		if (svm_get_cpl(vcpu) == 0)
+			error_code &= ~PFERR_USER_MASK;
+	}
+
 	if (sev_snp_guest(vcpu->kvm) && (error_code & PFERR_GUEST_ENC_MASK))
 		error_code |= PFERR_PRIVATE_ACCESS;
 
-- 
2.52.0