Re: [PATCH 1/4] x86/fpu: Clear XSTATE_BV[i] in save state whenever XFD[i]=1

[Paolo Bonzini]

On 1/15/26 17:07, Dave Hansen wrote:
> On 1/6/26 09:56, Jim Mattson wrote:
> > Apologies. You're right. Though Intel is a bit coy, the only way to
> > interpret that section of the SDM is to conclude that the AMX state in
> > the CPU becomes undefined when XFD[18] is set.
>
> I'll touch base with the folks that wrote that blurb. I'm a little
> nervous to interpret that "software should not..." blurb as a full
> architectural DANGER sign partly because it's in a "RECOMMENDATIONS FOR
> SYSTEM SOFTWARE" section.
>
> I'm _sure_ they discussed tying XFD[i] and XINUSE[i] together and there
> was a good reason they did not.

Is there anything that prevents an SMM handler (or more likely, an SMI 
transfer monitor) to do an XSAVE/XRSTOR and destroy tile data?

Paolo