linux-kernel - Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

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Message-ID: <CAHk-=wik5AfDs7qqjGHQ5vRBYkV8K6tFmPna3PdbwdzVwPGTsg@mail.gmail.com>
Date:   Thu, 29 Nov 2018 09:35:11 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Lutomirski <luto@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, mhiramat@...nel.org,
        jbaron@...mai.com, Jiri Kosina <jkosina@...e.cz>,
        David.Laight@...lab.com, bp@...en8.de, julia@...com,
        jeyu@...nel.org, Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64

On Thu, Nov 29, 2018 at 9:13 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> No, we really do need to sync after we change the second part of the
> command with the int3 on it. Unless there's another way to guarantee
> that the full instruction gets seen when we replace the int3 with the
> finished command.

Making sure the call instruction is aligned with the I$ fetch boundary
should do that.

It's not in the SDM, but neither was our current behavior - we
were/are just relying on "it will work".

                 Linus