linux-kernel - Re: [PATCH v13 00/16] Enable FSGSBASE instructions

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Message-ID: <CALCETrUeRPVq2n0UVuZZ9WTugH8Aetdw5rY+cccCT_=YgnJ_og@mail.gmail.com>
Date:   Thu, 18 Jun 2020 11:08:31 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Sasha Levin <sashal@...nel.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Tony Luck <tony.luck@...el.com>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: Re: [PATCH v13 00/16] Enable FSGSBASE instructions

On Thu, Jun 18, 2020 at 7:18 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Sasha,
>
> Sasha Levin <sashal@...nel.org> writes:
> > Changes from v12:
> >  - Reformat the series to be closer to the reverted codebase for easier
> >    review.
> >  - Drop a few of the changes introduced in v8 and v9.
>
> I've pushed the lot out to
>
>    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/fsgsbase
>
> Thanks for taking this up!
>

Is there a plan to deal with:

        /*
         * This function has some ABI oddities.
         *
         * A 32-bit ptracer probably expects that writing FS or GS will change
         * FSBASE or GSBASE respectively.  In the absence of FSGSBASE support,
         * this code indeed has that effect.  When FSGSBASE is added, this
         * will require a special case.
         *
         * For existing 64-bit ptracers, writing FS or GS *also* currently
         * changes the base if the selector is nonzero the next time the task
         * is run.  This behavior may? not be needed, and trying to preserve it
         * when FSGSBASE is added would be complicated at best.
         */

in arch/x86/kernel/ptrace.c?