linux-kernel - Re: [PATCH v4 5/5] x86: drop mfence in favor of lock+addl

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Message-ID: <20160127195314-mutt-send-email-mst@redhat.com>
Date:	Wed, 27 Jan 2016 19:56:37 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Davidlohr Bueso <dbueso@...e.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	virtualization <virtualization@...ts.linux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...nel.org>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v4 5/5] x86: drop mfence in favor of lock+addl

On Wed, Jan 27, 2016 at 09:37:45AM -0800, Linus Torvalds wrote:
> On Wed, Jan 27, 2016 at 7:10 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > -#define __smp_mb()     mb()
> > +#define __smp_mb()     asm volatile("lock; addl $0,-4(%%esp)" ::: "memory", "cc")
> 
> So this doesn't look right for x86-64. Using %esp rather than %rsp.
> How did that even work for you?
> 
>                 Linus

Oops, didn't test this version properly.
Pls disregard, I'll repost after some proper testing.

-- 
MST