KVM: Ignore PCI ECS I/O enablement

Linux guests will try to enable access to the extended PCI config space
via the I/O ports 0xCF8/0xCFC on AMD Fam10h CPU. Since we (currently?)
don't use ECS, simply ignore write and read attempts.
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -844,6 +844,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 			return 1;
 		}
 		break;
+	case MSR_AMD64_NB_CFG:
+		break;
 	case MSR_IA32_DEBUGCTLMSR:
 		if (!data) {
 			/* We support the non-activated case already */
@@ -1049,6 +1051,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
 	case MSR_P6_EVNTSEL1:
 	case MSR_K7_EVNTSEL0:
 	case MSR_K8_INT_PENDING_MSG:
+	case MSR_AMD64_NB_CFG:
 		data = 0;
 		break;
 	case MSR_MTRRcap: