Re: [PATCH v4 03/16] x86/alternatives: Disable LASS when patching kernel alternatives

[Kirill A. Shutemov]

On Wed, Jul 10, 2024 at 07:18:36PM +0200, Borislav Petkov wrote:
> On Wed, Jul 10, 2024 at 07:06:39PM +0300, Alexander Shishkin wrote:
> >  static void text_poke_memcpy(void *dst, const void *src, size_t len)
> >  {
> > -	memcpy(dst, src, len);
> > +	stac();
> > +	__inline_memcpy(dst, src, len);
> > +	clac();
> 
> I think you need LASS-specific stac()/clac() or an alternative_2 or so. You
> can't cause that perf penalty on !LASS machines.

Hm. Do we have text_poke() in hot path?

Even if we do, I doubt flipping AC flag would make any performance
difference in context of all locking and TLB flushing we do in this
codepath.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov