Re: [PATCH] x86/cpu: Enable STIBP if Automatic IBRS is enabled

[Kim Phillips]

On 7/20/23 3:58 PM, Jim Mattson wrote:
> On Thu, Jul 20, 2023 at 12:48 PM Kim Phillips <kim.phillips@xxxxxxx> wrote:
> > Unlike Intel's Enhanced IBRS feature, AMD's Automatic IBRS does not
> > provide protection to processes running at CPL3/user mode [1].
> >
> > Explicitly enable STIBP to protect against cross-thread CPL3
> > branch target injections on systems with Automatic IBRS enabled.
>
> Is there any performance penalty to enabling STIBP + AUTOIBRS, aside
> from the lost sharing?

Not to my knowledge.

> Or does this just effectively tag the branch
> prediction information with thread ID?

I don't know the implementation, but AFAIK, AUTOIBRS and STIBP
are independent of each other.

Thanks,

Kim