From: William Roche Date: Tue, 17 Mar 2026 10:38:10 +0000 (+0000) Subject: x86/mce/amd: Check SMCA feature bit before accessing SMCA MSRs X-Git-Tag: v7.0-rc5~5^2~2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=201bc182ad6333468013f1af0719ffe125826b6a;p=thirdparty%2Fkernel%2Flinux.git x86/mce/amd: Check SMCA feature bit before accessing SMCA MSRs People do effort to inject MCEs into guests in order to simulate/test handling of hardware errors. The real use case behind it is testing the handling of SIGBUS which the memory failure code sends to the process. If that process is QEMU, instead of killing the whole guest, the MCE can be injected into the guest kernel so that latter can attempt proper handling and kill the user *process* in the guest, instead, which caused the MCE. The assumption being here that the whole injection flow can supply enough information that the guest kernel can pinpoint the right process. But that's a different topic... Regardless of virtualization or not, access to SMCA-specific registers like MCA_DESTAT should only be done after having checked the smca feature bit. And there are AMD machines like Bulldozer (the one before Zen1) which do support deferred errors but are not SMCA machines. Therefore, properly check the feature bit before accessing related MSRs. [ bp: Rewrite commit message. ] Fixes: 7cb735d7c0cb ("x86/mce: Unify AMD DFR handler with MCA Polling") Signed-off-by: William Roche Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Yazen Ghannam Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20260218163025.1316501-1-william.roche@oracle.com --- diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c index da13c1e37f87..a030ee4cecc2 100644 --- a/arch/x86/kernel/cpu/mce/amd.c +++ b/arch/x86/kernel/cpu/mce/amd.c @@ -875,13 +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); + 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; + /* 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); }