Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

[Thomas Gleixner]

On Tue, 20 Nov 2018, Jiri Kosina wrote:

> On Tue, 20 Nov 2018, Thomas Gleixner wrote:
> 
> > What? IBPB makes tons of sense even without STIBP.
> 
> On non-SMT, yes. But this patchset ties those two the other (sensible) way 
> around AFAICS ("STIBP iff (IBPB && SMT)").

Errm. No.

The patches disable IBPB if STIBP is not available and that has absolutely
nothing to do with SMT simply because the static key controlling IBPB is
only flipped on when both IBPB and STIBP are available.

For SMT=off STIBP is pointless, but IBPB still makes a lot of sense.

That's a change which is neither documented nor correct.

Thanks,

	tglx