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KVM: SVM: work around errata 1218

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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.

Tested-by: David Riley <d.riley@proxmox.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2026-04-08 11:42:16 -04:00
parent fe080f58de
commit 878fffd76c
1 changed files with 12 additions and 0 deletions
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12
arch/x86/kvm/svm/svm.c
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@ -1993,6 +1993,18 @@ static int npf_interception(struct kvm_vcpu *vcpu)
}
}
if (!is_sev_es_guest(vcpu) &&
(svm->vmcb->control.misc_ctl & SVM_MISC_ENABLE_GMET) &&
(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) != 3)
error_code &= ~PFERR_USER_MASK;
}
if (is_sev_snp_guest(vcpu) && (error_code & PFERR_GUEST_ENC_MASK))
error_code |= PFERR_PRIVATE_ACCESS;