Re: [PATCH v3 1/1] x86/mce/amd: Guard SMCA DESTAT access on non-SMCA machines

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

On 3/17/26 14:32, Borislav Petkov wrote:
> On Tue, Mar 17, 2026 at 10:38:10AM +0000, “William Roche wrote:
>> From: William Roche <william.roche@oracle.com>
>>
>> Access to SMCA specific registers like MCA_DESTAT should only be done
>> after having checked the smca bit. Avoiding a non-SMCA machine (like
>> AMD QEMU/KVM VMs) crash during deferred error handling.
> 
> Not good enough. I rewrote it to:
> 
> Author: William Roche <william.roche@oracle.com>
> Date:   Tue Mar 17 10:38:10 2026 +0000
>   
>      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 real hardware errors. These efforts are of a questionable nature because,
>      for one, a guest cannot really make any assumptions about the underlying
>      machine and especially which MSR accesses the hypervisor filters and
>      which it doesn't. See Link tag for the whole background.
>      
>      However, 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 <william.roche@oracle.com>
>      Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
>      Reviewed-by: Yazen Ghannam <yazen.ghannam@amd.com>
>      Cc: stable@vger.kernel.org
>      Link: https://lore.kernel.org/r/20260218163025.1316501-1-william.roche@oracle.com

Thank you.

William.