linux-kernel - Re: [PATCH 3/16] read/write_crX, clts and wbinvd for 64-bit paravirt

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Message-ID: <C34FAA4C.17CA9%Keir.Fraser@cl.cam.ac.uk>
Date:	Thu, 01 Nov 2007 16:07:40 +0000
From:	Keir Fraser <Keir.Fraser@...cam.ac.uk>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Glauber de Oliveira Costa <gcosta@...hat.com>
CC:	<lguest@...abs.org>, <kvm-devel@...ts.sourceforge.net>,
	<linux-kernel@...r.kernel.org>, <ak@...e.de>,
	<chrisw@...s-sol.org>, <tglx@...utronix.de>,
	<anthony@...emonkey.ws>, <akpm@...ux-foundation.org>,
	<virtualization@...ts.linux-foundation.org>, <mingo@...e.hu>
Subject: Re: [PATCH 3/16] read/write_crX, clts and wbinvd for 64-bit
 paravirt

On 1/11/07 15:30, "Jeremy Fitzhardinge" <jeremy@...p.org> wrote:

> Glauber de Oliveira Costa wrote:
>> I in fact have seen bugs with mixed reads and writes to the same cr,
>> (cr4), but adding the volatile
>> flag to the read function seemed to fix it.
> 
> Well, volatile will make a read be repeated rather than caching the
> previous value, but it has no effect on ordering.

volatile prevents the asm from being 'moved significantly', according to the
gcc manual. I take that to mean that reordering is not allowed.

 -- Keir


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