[PATCH] x86: Support BHI_CTRL instruction

[Jiang, Haochen]

> From: Jan Beulich <jbeulich@suse.com>
> Sent: Wednesday, August 5, 2026 4:50 PM
> 
> On 03.06.2026 10:08, Jan Beulich wrote:
> > On 03.06.2026 09:47, Jiang, Haochen wrote:
> >> This let me further wonder if a user input something like "{rex2} ibhf",
> >> should we accept that? Let me double check that.
> >
> > We should accept it if the resulting encoding does what is intended / written.
> > According to Christian's reply REX2.W doesn't have the same effect, but I wonder
> > if it's really sensible that way. The W bits, whether encoded in REX or REX2,
> > really ought to have the same meaning as per the APX spec. Unless of course this
> > is indeed meant to be another special case besides PUSHP/POPP (when imo it would
> > be really nice if special cases were avoided whenever possible).
> 
> Has this been clarified in the meantime? It's somewhat sad that 2.47 shipped
> without this addition, when that has been missing for quite some time.

I have got an internal clarification for BHI_CTRL, pending for documentation
change. REX.W and REX2.W should have the same effect. But it will take some
time. I planned to mention it in my updated patch.

Thx,
Haochen