[PATCH] KVM: allow bit 10 to be cleared in MSR_IA32_MC4_CTL

[Andre Przywara <andre.przywara@amd.com>]

There is a quirk for AMD K8 CPUs in many Linux kernels (see
arch/x86/kernel/cpu/mcheck/mce.c:__mcheck_cpu_apply_quirks()) that
clears bit 10 in that MCE related MSR. KVM can only cope with all
zeros or all ones, so it will inject a #GP into the guest, which
will let it panic.
So lets add a quirk to the quirk and ignore this single cleared bit.
This fixes -cpu kvm64 on all machines and -cpu host on K8 machines
with some guest Linux kernels.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 arch/x86/kvm/x86.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 097ad3a..a58c634 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -910,9 +910,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		if (msr >= MSR_IA32_MC0_CTL &&
 		    msr < MSR_IA32_MC0_CTL + 4 * bank_num) {
 			u32 offset = msr - MSR_IA32_MC0_CTL;
-			/* only 0 or all 1s can be written to IA32_MCi_CTL */
+			/* only 0 or all 1s can be written to IA32_MCi_CTL
+			 * some Linux kernels though clear bit 10 in bank 4 to
+			 * workaround a BIOS/GART TBL issue on AMD K8s, ignore
+			 * this to avoid an uncatched #GP in the guest
+			 */
 			if ((offset & 0x3) == 0 &&
-			    data != 0 && data != ~(u64)0)
+			    data != 0 && (data | (1 << 10)) != ~(u64)0)
 				return -1;
 			vcpu->arch.mce_banks[offset] = data;
 			break;
-- 
1.6.4