linux-kernel - Re: [PATCH] x86/bugs: Allow STIBP with IBRS

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Message-ID: <CACYkzJ6p0+bTjbAyv6PD+ZKyyfjM9NyvtuMB-vwNHkeWm72B7A@mail.gmail.com>
Date:   Mon, 20 Feb 2023 11:04:56 -0800
From:   KP Singh <kpsingh@...nel.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        pjt@...gle.com, evn@...gle.com, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, peterz@...radead.org,
        pawan.kumar.gupta@...ux.intel.com, kim.phillips@....com,
        alexandre.chartre@...cle.com, daniel.sneddon@...ux.intel.com,
        José Oliveira <joseloliveira11@...il.com>,
        Rodrigo Branco <rodrigo@...nelhacking.com>,
        Alexandra Sandulescu <aesa@...gle.com>,
        Jim Mattson <jmattson@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/bugs: Allow STIBP with IBRS

On Mon, Feb 20, 2023 at 11:00 AM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> On Mon, Feb 20, 2023 at 10:33:56AM -0800, KP Singh wrote:
> >  static char *stibp_state(void)
> >  {
> > -       if (spectre_v2_in_ibrs_mode(spectre_v2_enabled))
> > +       if (!spectre_v2_user_needs_stibp(spectre_v2_enabled))
> >                 return "";
> >
> >         switch (spectre_v2_user_stibp) {
> >
> > Also Josh, is it okay for us to have a discussion and have me write
> > the patch as a v2? Your current patch does not even credit me at all.
> > Seems a bit unfair, but I don't really care. I was going to rev up the
> > patch with your suggestions.
>
> Well, frankly the patch needed a complete rewrite.  The patch
> description was unclear about what the problem is and what's being

Josh, this is a complex issue, we are figuring it out together on the
list. It's complex, that's why folks got it wrong in the first place.
Calling the patch obtuse and unclear is unfair!

> fixed.  The code was obtuse and the comments didn't help.  I could tell
> by the other replies that I wasn't the only one confused.

The patch you sent is not clear either, it implicitly ties in STIBP
with eIBRS. There is no explanation anywhere that IBRS just means
KERNEL_IBRS.

>
> I can give you Reported-by, or did you have some other tag in mind?
>
> --
> Josh