linux-kernel - Re: [GIT PULL] x86/asm changes for v5.6

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Message-ID: <CAHk-=wh9xdJzfcPU4e4diAZDtUJVg+SSocoYP+aVYWnDZd-UMQ@mail.gmail.com>
Date:   Thu, 30 Jan 2020 10:02:54 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     "Luck, Tony" <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86/asm changes for v5.6

On Thu, Jan 30, 2020 at 9:39 AM Borislav Petkov <bp@...e.de> wrote:
>
> Yeah, makes sense. It would help if one slaps a relative JMP as *not*
> the first insn in an alternatives replacement and the build to warn that
> it can't work.

Maybe with the exception that a short conditional jump inside the
alternative code itself is fine.

Because a branch-over inside the alternative sequence (or a loop -
think inline cmpxchg loop or whatever) would be fine, since it's
unaffected by code placement.

              Linus