Re: [PATCH] libx86: Introduce x86_cpu_policy_calculate_compatible() with MSR_ARCH_CAPS handling

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.05.2021 16:50, Andrew Cooper wrote:
> On 05/05/2021 15:48, Jan Beulich wrote:
>> On 05.05.2021 16:29, Andrew Cooper wrote:
>>> Technically, MCXSR_MASK is also a hard blocker to migration, but we
>>> don't even have that data in a consumable form, and we just might be
>>> extremely lucky and discover that it is restricted to non-64-bit CPUs.
>> "it" being what here? The value's presence / absence in an {F,}XSAVE
>> image? Or the precise value of it?
> 
> The precise value of it.

Not sure whether DAZ is new enough, but relatively sure MM isn't.

>  Migrating across the boundary where the
> default changed will cause {F,}RSTOR instructions to #GP.

That's understood. Is there actually anything standing in the way
of treating MXCSR_MASK like yet another feature flag group?

Jan