Re: [PATCH v3 2/6] x86/bugs: Use SBPB in __write_ibpb() if applicable

[Josh Poimboeuf]

On Wed, Apr 02, 2025 at 03:41:25PM -0500, Tom Lendacky wrote:
> On 4/2/25 13:19, Josh Poimboeuf wrote:
> > __write_ibpb() does IBPB, which (among other things) flushes branch type
> > predictions on AMD.  If the CPU has SRSO_NO, or if the SRSO mitigation
> > has been disabled, branch type flushing isn't needed, in which case the
> > lighter-weight SBPB can be used.
> 
> Maybe add something here that indicates the x86_pred_cmd variable tracks
> this optimization so switch to using that variable vs the hardcoded IBPB?

Indeed, adding a second paragraph to clarify that:

  x86/bugs: Use SBPB in write_ibpb() if applicable

  write_ibpb() does IBPB, which (among other things) flushes branch type
  predictions on AMD.  If the CPU has SRSO_NO, or if the SRSO mitigation
  has been disabled, branch type flushing isn't needed, in which case the
  lighter-weight SBPB can be used.

  The 'x86_pred_cmd' variable already keeps track of whether IBPB or SBPB
  should be used.  Use that instead of hardcoding IBPB.

-- 
Josh