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

[Paolo Bonzini]

On Thu, Jan 8, 2026 at 4:08 AM Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx> wrote:
> > +     /*
> > +      * KVM's guest ABI is that setting XFD[i]=1 *can* immediately revert
> > +      * the save state to initialized.  Likewise, KVM_GET_XSAVE does the
>
> Nit:
> To me "initialized" has the implication that it's active.
> I prefer the description "initial state" or "initial configuration" used in
> SDM here.
> I am not a native English speaker though, please ignore it if it's just my
> feeling.

Sure, why not:

   KVM's guest ABI is that setting XFD[i]=1 *can* immediately revert the
   save state to its initial configuration.  Likewise, KVM_GET_XSAVE does
   the same as XSAVE and returns XSTATE_BV[i]=0 whenever XFD[i]=1.

> > +     /*
> > +      * Do not reject non-initialized disabled features for backwards
> > +      * compatibility, but clear XSTATE_BV[i] whenever XFD[i]=1.
> > +      * Otherwise, XRSTOR would cause a #NM.
> > +      */

Same here:

   For backwards compatibility, do not expect disabled features to be in
   their initial state.  XSTATE_BV[i] must still be cleared whenever
   XFD[i]=1, or XRSTOR would cause a #NM.

Thanks!

Paolo