KVM: SVM: WARN if KVM attempts emulation on #UD or #GP for SEV guests

WARN if KVM attempts to emulate in response to #UD or #GP for SEV guests,
i.e. if KVM intercepts #UD or #GP, as emulation on any fault except #NPF
is impossible since KVM cannot read guest private memory to get the code
stream, and the CPU's DecodeAssists feature only provides the instruction
bytes on #NPF.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Message-Id: <20220120010719.711476-7-seanjc@google.com>
[Warn on EMULTYPE_TRAP_UD_FORCED according to Liam Merwick's review. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 115743e250bbe1f98cffb7c5cd9c361353221707..85bbfba1fa077507f72416852e33219b08f8f60a 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4268,6 +4268,11 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
        if (!sev_guest(vcpu->kvm))
                return true;
 
+       /* #UD and #GP should never be intercepted for SEV guests. */
+       WARN_ON_ONCE(emul_type & (EMULTYPE_TRAP_UD |
+                                 EMULTYPE_TRAP_UD_FORCED |
+                                 EMULTYPE_VMWARE_GP));
+
        /*
         * Emulation is impossible for SEV-ES guests as KVM doesn't have access
         * to guest register state.