Re: [PATCH 2/2] x86/cpu: Skip reading MSR_IA32_PLATFORM_ID in virtualized environment

[Edgecombe, Rick P]

On Tue, 2026-04-28 at 14:01 +0800, Xiaoyao Li wrote:
> > +	/* Don't try to read microcode bits when virtualized. */
> 
> The platform ID is not only used by microcode update.

From the series with the blamed commit:
   Today, the only code that cares about the platform ID is the microcode
   update code itself. To facilitate storing the platform ID in a more
   generic place and using it outside of the microcode update itself, put
   the enumeration into a helper function.
   
But it is still only used for microcode stuff AFAICT... It seems it was just
moved to be "consistent with the other fields which can be matched".

>  I don't think 
> calling them microcode bits is proper. It's also stashed in struct 
> cpuinfo_x86::intel_platform_id and used in x86_match_cpu() as a factor 
> as the generic FMS (Family, Model, Stepping) bits.
> 
> We skip things due to hypervisor is set usually when the thing is known 
> unable to be virtualized. From the perspective of microcode update, it's 
> OK to skip reading it due to hypervisor bit. However, from the 
> perspective of generic platform ID, it seems not that reasonable to skip 
> reading it due to hypervisor bit. Especially KVM has supported this MSR 
> for normal VMs.
> 
> So how about using the safe version of RDMSR, if we want the enhancement?

With the check if we are not virtualized we can get a nice warning if run on
some weird platform with this MSR missing.