linux-kernel - Re: [patch 02/38] x86/cpu: Use native_wrmsrl() in load_percpu

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Message-ID: <CAHk-=wiAF9KF5x8A8QW+=k_XFyaMgjS74h7gmHRYBB+PXkQ2rQ@mail.gmail.com>
Date:   Sun, 17 Jul 2022 08:20:46 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrew Cooper <Andrew.Cooper3@...rix.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch 02/38] x86/cpu: Use native_wrmsrl() in load_percpu_segment()

On Sat, Jul 16, 2022 at 5:22 PM Andrew Cooper <Andrew.Cooper3@...rix.com> wrote:
>
> It's only 32bit where the percpu pointer is tied to the GDT.  On 64bit,
> gsbase is good before this, and remains good after.

That sounds sensible to me, but somebody should check that there's
nothing that accidentally relied on the MSR_GS_BASE setting (or the
segment selector clearing, for that matter).

Not that I can necessarily see how anything could work with it wrong, but..

           Linus