linux-kernel - Re: [PATCH v3 5/6] x86/alternative: Use a single access in text

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Message-ID: <20190110132409.641dbca8@gandalf.local.home>
Date:   Thu, 10 Jan 2019 13:24:09 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Nadav Amit <namit@...are.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>, Jiri Kosina <jkosina@...e.cz>,
        David Laight <David.Laight@...LAB.COM>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Edward Cree <ecree@...arflare.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v3 5/6] x86/alternative: Use a single access in
 text_poke() where possible

On Thu, 10 Jan 2019 10:04:28 -0800
Sean Christopherson <sean.j.christopherson@...el.com> wrote:

> > What atomicity guarantee does the above require?  
> 
> I was asking in the context of static calls.  My understanding is that
> the write to change the imm32 of the CALL needs to be atomic from a
> code fetch perspective so that we don't jump to a junk address.
> 
> Or were you saying that Intel gave an official OK on text_poke_bp()?

Yes, the latter. I was talking about Intel giving the official OK for
text_poke_bp().

-- Steve