Re: [PATCH] x86/bugs: Switch to "auto" when "ibrs" selected on Enhanced IBRS parts

From: Josh Poimboeuf
Date: Thu Jul 14 2022 - 13:38:21 EST

On Thu, Jul 14, 2022 at 07:03:32PM +0200, Peter Zijlstra wrote:
> On Thu, Jul 14, 2022 at 09:01:06AM -0700, Josh Poimboeuf wrote:
> > > Yeah this; if the user asks for IBRS, we should give him IBRS. I hate
> > > the 'I know better, let me change that for you' mentality.
> >
> > eIBRS CPUs don't even have legacy IBRS so I don't see how this is even
> > possible.
> You can still WRMSR a lot on them. Might not make sense but it 'works'.

Even in Intel documentation, eIBRS is often referred to as IBRS. It
wouldn't be surprising for a user to consider spectre_v2=ibrs to mean
"use eIBRS".

I'm pretty sure there's nobody out there that wants spectre_v2=ibrs to
mean "make it slower and possibly less secure because it's being used
contrary to the spec".