[PATCH v1 1/1] x86/mce: AMD deferred error handling crashes Qemu VMs

["“William Roche" <william.roche@oracle.com>]

From: William Roche <william.roche@oracle.com>

A non Scalable MCA system may prevent access to SMCA specific registers
like MCA_DESTAT. This is the case of Qemu/kvm VMs, and the VM kernel
needs to avoid accessing SMCA registers on non-SMCA platforms.

Fixes: 7cb735d7c0cb ("x86/mce: Unify AMD DFR handler with MCA Polling")
Cc: stable@vger.kernel.org
Signed-off-by: William Roche <william.roche@oracle.com>
---
 arch/x86/kernel/cpu/mce/amd.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 3f1dda355307..53c4b032ad35 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -875,14 +875,18 @@ void amd_clear_bank(struct mce *m)
 {
 	amd_reset_thr_limit(m->bank);
 
-	/* Clear MCA_DESTAT for all deferred errors even those logged in MCA_STATUS. */
-	if (m->status & MCI_STATUS_DEFERRED)
-		mce_wrmsrq(MSR_AMD64_SMCA_MCx_DESTAT(m->bank), 0);
-
-	/* Don't clear MCA_STATUS if MCA_DESTAT was used exclusively. */
-	if (m->kflags & MCE_CHECK_DFR_REGS)
-		return;
+	if (mce_flags.smca) {
+		/*
+		 * Clear MCA_DESTAT for all deferred errors even those
+		 * logged in MCA_STATUS.
+		 */
+		if (m->status & MCI_STATUS_DEFERRED)
+			mce_wrmsrq(MSR_AMD64_SMCA_MCx_DESTAT(m->bank), 0);
 
+		/* Don't clear MCA_STATUS if MCA_DESTAT was used exclusively. */
+		if (m->kflags & MCE_CHECK_DFR_REGS)
+			return;
+	}
 	mce_wrmsrq(mca_msr_reg(m->bank, MCA_STATUS), 0);
 }
 
-- 
2.47.3