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From:   Andy Lutomirski <luto@kernel.org>
Date:   Fri, 30 Nov 2018 12:18:33 -0800
Message-ID: <CALCETrVwdtLnnLR7Qb3LVCHDRpJ-cgU28jiGOQdaPFLVSvvZXA@mail.gmail.com>
Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call
 implementation for x86-64
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
        David Laight <David.Laight@aculab.com>,
        Borislav Petkov <bp@alien8.de>, julia@ni.com, jeyu@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>
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On Fri, Nov 30, 2018 at 11:51 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, Nov 30, 2018 at 10:39 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > AFAICT, all the other proposed options seem to have major issues.
>
> I still absolutely detest this patch, and in fact it got worse from
> the test of the config variable.
>
> Honestly, the entry code being legible and simple is more important
> than the extra cycle from branching to a trampoline for static calls.
>
> Just don't do the inline case if it causes this much confusion.

With my entry maintainer hat on, I don't mind it so much, although the
implementation needs some work.  The #ifdef should just go away, and
there should be another sanity check in the sanity check section.

Or we could replace that IPI with x86's bona fide serialize-all-cpus
primitive and then we can just retry instead of emulating.  It's a
piece of cake -- we just trigger an SMI :)  /me runs away.

--Andy