KVM: ignore AMDs HWCR register access to set the FFDIS bit

Linux tries to disable the flush filter on all AMD K8 CPUs. Since KVM
does not handle the needed MSR, the injected #GP will panic the Linux
kernel. Ignore setting of the HWCR.FFDIS bit in this MSR to let Linux
boot with an AMD K8 family guest CPU.
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/svm.c

@@ -2137,7 +2137,6 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, unsigned ecx, u64 data)
 		break;
 	case MSR_VM_CR:
 	case MSR_VM_IGNNE:
-	case MSR_K7_HWCR:
 		pr_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
 		break;
 	default:

arch/x86/kvm/x86.c

@@ -833,6 +833,14 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 	case MSR_EFER:
 		set_efer(vcpu, data);
 		break;
+	case MSR_K7_HWCR:
+		data &= ~(u64)0x40;	/* ignore flush filter disable */
+		if (data != 0) {
+			pr_unimpl(vcpu, "unimplemented HWCR wrmsr: 0x%llx\n",
+				data);
+			return 1;
+		}
+		break;
 	case MSR_IA32_DEBUGCTLMSR:
 		if (!data) {
 			/* We support the non-activated case already */