linux-kernel - Re: [PATCH 3/4] x86,asm: Re-work smp_store

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Message-ID: <CA+55aFwUHWb+y2gtKp55mwqocTjYv2xWzosvtO4K97VzPmfUSA@mail.gmail.com>
Date:	Wed, 13 Jan 2016 10:38:10 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andy Lutomirski <luto@...nel.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Davidlohr Bueso <dbueso@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 3/4] x86,asm: Re-work smp_store_mb()

On Wed, Jan 13, 2016 at 8:42 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
>
> Oh, I think this means we need a "cc" clobber.

It's probably a good idea to add one.

Historically, gcc doesn't need one on x86, and always considers flags
clobbered. We are probably missing the cc clobber in a *lot* of places
for this reason.

But even if not necessary, it's probably a good thing to add for
documentation, and in case gcc semantcs ever change.

                  Linus