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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Sasha Levin <sashal@kernel.org>,
        Andrew Lutomirski <luto@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        X86 ML <x86@kernel.org>, Shuah Khan <shuah@kernel.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Tony Luck <tony.luck@intel.com>,
        "Bae\, Chang Seok" <chang.seok.bae@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "open list\:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Subject: Re: [PATCH v13 00/16] Enable FSGSBASE instructions
In-Reply-To: <CALCETrUeRPVq2n0UVuZZ9WTugH8Aetdw5rY+cccCT_=YgnJ_og@mail.gmail.com>
References: <20200528201402.1708239-1-sashal@kernel.org> <874kr8cv9i.fsf@nanos.tec.linutronix.de> <CALCETrUeRPVq2n0UVuZZ9WTugH8Aetdw5rY+cccCT_=YgnJ_og@mail.gmail.com>
Date:   Thu, 18 Jun 2020 20:25:30 +0200
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Andy Lutomirski <luto@kernel.org> writes:
> 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?

Not that I'm aware of.