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

[Yazen Ghannam <yazen.ghannam@amd.com>]

On Fri, Feb 13, 2026 at 06:26:30PM +0000, “William Roche wrote:
> From: William Roche <william.roche@oracle.com>
> 

Hi William, I agree with the fix, and feedback is mostly around
style/convention.

Use "x86/mce/amd" as the $SUBJECT prefix.

Subject should be imperative.

Ex. "x86/mce/amd: Fix VM crash during deferred error handling"

> 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

I expect that QEMU and KVM should be capitalized.

> needs to avoid accessing SMCA registers on non-SMCA platforms.
> 

The commit message should include an imperative statement.

Ex. "Check for the SMCA feature before accessing MCA_DESTAT."

> 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>

"CC stable" tag should go after Signed-off-by.

> ---
>  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;
> +	}

Please include a newline here.

>  	mce_wrmsrq(mca_msr_reg(m->bank, MCA_STATUS), 0);
>  }
>  

Otherwise, looks good to me.

Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>

Thanks,
Yazen