Re: [PATCH v2] KVM: x86: Remove AMX-TF32 enumeration

On Tue, Aug 18, 2026, Christian Ludloff wrote:
> On Tue, Aug 18, 2026 at 5:55 PM Dave Hansen <[email protected]> wrote:
> > On 7/24/26 08:37, Christian Ludloff wrote:
> > >> My understanding is that the revert was considered because TF32 never
> > >> reached any implementation. If that's incorrect, I'd certainly welcome a
> > >> correction.
> > > Both TF32 and TRANSPOSE made it into a product that shipped.
> > >
> > > Not from Intel... but.
> > >
> > > So their CPUID feature flags and their opcodes aren't reclaimable
> > > and efforts to rip out their software support are counterproductive.
> >
> > What would folks' preference be on how Intel should document this going
> > forward? Just leave it as it as enumerating TF32?
> >
> > There are notes in the SDM like:
> >
> >         Intel® MPX has been deprecated and will not be available on any
> >         future processors.
> >
> > There could be a note like that for the TF32, I would imagine.
> 
> Yes, that terse sentence works.
>   Once for AMX-TRANSPOSE.
>   Once for AMX-TF32.

Maybe use a similar approach as is done for the HYPERVISOR bit (0x1.ECX[31), and
have the "Field Name" entry say Not Used, and then use the "Description" to explain
why?  E.g.

  Register        Field Name      Description                             Domain
  EAX[6]          Not Used        Intel processors always return 0.       Platform
                                  Allocated for backwards compatibility
                                  with software that expects this to
                                  enumerate AMX_TF32.

Or Christian's terse version (I kinda like the terse version).

  Register        Field Name      Description                             Domain
  EAX[6]          Not Used        Intel processors always return 0.       Platform
                                  Once for AMX_TF32.

 
> If you want the back references:
>   TRANSPOSE got dropped from ISE #059 and APX #007.
>   TF32 got dropped from ISE #062.
> 
> In terms of the opcodes, it is like MPX too: no recycling for
> a long time. Luckily there is plenty of remaining space.
> 
> --
> C.