KVM: svm: writes to MSR_K7_HWCR generates GPE in guest

Since commit 575203 the MCE subsystem in the Linux kernel for AMD sets bit 18
in MSR_K7_HWCR. Running such a kernel as a guest in KVM on an AMD host results
in a GPE injected into the guest because kvm_set_msr_common returns 1. This
patch fixes this by masking bit 18 from the MSR value desired by the guest.
Signed-off-by: Matthias Lange <matthias.lange@kernkonzept.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -2035,6 +2035,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		data &= ~(u64)0x40;	/* ignore flush filter disable */
 		data &= ~(u64)0x100;	/* ignore ignne emulation enable */
 		data &= ~(u64)0x8;	/* ignore TLB cache disable */
+		data &= ~(u64)0x40000;  /* ignore Mc status write enable */
 		if (data != 0) {
 			vcpu_unimpl(vcpu, "unimplemented HWCR wrmsr: 0x%llx\n",
 				    data);