linux-kernel - Re: [PATCH stable 5.4,5.10] x86/fpu: Correct pkru/xstate inconsistency

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Date:   Wed, 16 Feb 2022 11:05:31 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Brian Geffon <bgeffon@...gle.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Willis Kung <williskung@...gle.com>,
        Guenter Roeck <groeck@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        "# v4 . 10+" <stable@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH stable 5.4,5.10] x86/fpu: Correct pkru/xstate
 inconsistency

On Tue, Feb 15, 2022 at 09:01:54PM -0500, Brian Geffon wrote:
> On Tue, Feb 15, 2022 at 4:42 PM Dave Hansen <dave.hansen@...el.com> wrote:
> >
> > On 2/15/22 13:32, Brian Geffon wrote:
> > >> How was this tested, and what do the maintainers of this subsystem
> > >> think?  And will you be around to fix the bugs in this when they are
> > >> found?
> > > This has been trivial to reproduce, I've used a small repro which I've
> > > put here: https://gist.github.com/bgaff/9f8cbfc8dd22e60f9492e4f0aff8f04f
> > > , I also was able to reproduce this using the protection_keys self
> > > tests on a 11th Gen Core i5-1135G7.
> >
> > I've got an i7-1165G7, but I'm not seeing any failures on a
> > 5.11 distro kernel.
> >
> 
> Hi Dave,
> I suspect the reason you're not seeing it is toolchain related, I'm
> building with clang 14.0.0 and it produces the sequence of
> instructions which use the cached value. Let me know if there is
> anything I can do to help you investigate this further.

Do older versions of clang have this problem?

thanks,

greg k-h