Re: [PATCH 10/12] x86/mcheck: Migrate vendor checks to use cpu_vendor()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.02.2026 13:02, Jan Beulich wrote:
> On 06.02.2026 17:15, Alejandro Vallejo wrote:
>> @@ -862,7 +861,7 @@ static void x86_mcinfo_apei_save(
>>      memset(&m, 0, sizeof(struct mce));
>>  
>>      m.cpu = mc_global->mc_coreid;
>> -    m.cpuvendor = boot_cpu_data.x86_vendor;
>> +    m.cpuvendor = cpu_vendor();
>>      m.cpuid = cpuid_eax(1);
>>      m.socketid = mc_global->mc_socketid;
>>      m.apicid = mc_global->mc_apicid;
>> @@ -964,7 +963,7 @@ static void cf_check __maybe_unused 
>> do_mc_get_cpu_info(void *v)
>>                          &xcp->mc_ncores_active, &xcp->mc_nthreads);
>>      xcp->mc_cpuid_level = c->cpuid_level;
>>      xcp->mc_family = c->x86;
>> -    xcp->mc_vendor = c->x86_vendor;
>> +    xcp->mc_vendor = cpu_vendor();
>>      xcp->mc_model = c->x86_model;
>>      xcp->mc_step = c->x86_mask;
>>      xcp->mc_cache_size = c->x86_cache_size;
> 
> What we do internally is one thing. But what we report to the outside 
> shouldn't
> be inaccurate, imo.

There may be an underlying issue here: For the former case, struct mce is an
entirely private definition, having in particular:

    uint8_t  cpuvendor;        /* cpu vendor as encoded in system.h */

which pretty clearly was inherited from Linux, and hence was broken when we
disconnected our X86_VENDOR_* values from Linux'es (in 4.9).

For the latter case, xen_mc_logical_cpu_t is part of the Xen ABI, and hence
it got screwed not only as per above, but another time when we converted
X86_VENDOR_* values from enumeration-like to bitfield-like (in 4.13).

Question of course is - if there were any consumers, they may have followed
our breaking of things. So it's hard to tell whether fixing might do more
bad than good. (I'll make a fix nevertheless, just in case).

Jan