[PATCH v2 2/2] KVM: x86: Do not gate MCE logging based on IA32_MCi_CTL

[Carlos López]

When userspace issues KVM_X86_SET_MCE, kvm_vcpu_ioctl_x86_set_mce()
decides whether to log an uncorrectable MCE by looking at the
corresponding IA32_MCi_CTL MSR. This is not the behavior specified in
the Intel SDM (17.3.2.1 IA32_MCi_CTL MSRs):

  Setting an EEj flag enables signaling #MC of the associated error and
  clearing it disables signaling of the error. Error logging happens
  regardless of the setting of these bits. The processor drops writes to
  bits that are not implemented.

Hoist the logging code, which writes to the corresponding error banks,
above the MCi_CTL check. Keep the #MC delivery after the check, as this
is correct behavior.

Fixes: 890ca9aefa78 ("KVM: Add MCE support")
Signed-off-by: Carlos López <clopez@xxxxxxx>
---
 arch/x86/kvm/x86.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 77a780177c4e..722bead405b5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5485,24 +5485,31 @@ static int kvm_vcpu_ioctl_x86_set_mce(struct kvm_vcpu *vcpu,
 	if ((mce->status & MCI_STATUS_UC) && (mcg_cap & MCG_CTL_P) &&
 	    vcpu->arch.mcg_ctl != ~(u64)0)
 		return 0;
-	/*
-	 * if IA32_MCi_CTL is not all 1s, the uncorrected error
-	 * reporting is disabled for the bank
-	 */
-	if ((mce->status & MCI_STATUS_UC) && banks[0] != ~(u64)0)
-		return 0;
+
 	if (mce->status & MCI_STATUS_UC) {
+		/*
+		 * Per the SDM, error logging always happens independently of
+		 * IA32_MCi_CTL
+		 */
+		if (banks[1] & MCI_STATUS_VAL)
+			mce->status |= MCI_STATUS_OVER;
+		banks[2] = mce->addr;
+		banks[3] = mce->misc;
+		banks[1] = mce->status;
+
+		/*
+		 * if IA32_MCi_CTL is not all 1s, the uncorrected error
+		 * reporting is disabled for the bank
+		 */
+		if (banks[0] != ~(u64)0)
+			return 0;
+
 		if ((vcpu->arch.mcg_status & MCG_STATUS_MCIP) ||
 		    !kvm_is_cr4_bit_set(vcpu, X86_CR4_MCE)) {
 			kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 			return 0;
 		}
-		if (banks[1] & MCI_STATUS_VAL)
-			mce->status |= MCI_STATUS_OVER;
-		banks[2] = mce->addr;
-		banks[3] = mce->misc;
 		vcpu->arch.mcg_status = mce->mcg_status;
-		banks[1] = mce->status;
 		kvm_queue_exception(vcpu, MC_VECTOR);
 	} else if (!(banks[1] & MCI_STATUS_VAL)
 		   || !(banks[1] & MCI_STATUS_UC)) {
-- 
2.51.0