linux-kernel - Re: [PATCH 03 of 36] x86: add memory barriers to wrmsr

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Message-ID: <20080625153136.2b3b6737@infradead.org>
Date:	Wed, 25 Jun 2008 15:31:36 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	x86@...nel.org, xen-devel <xen-devel@...ts.xensource.com>,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>
Subject: Re: [PATCH 03 of 36] x86: add memory barriers to wrmsr

On Wed, 25 Jun 2008 14:08:57 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Arjan van de Ven wrote:
> > it's more readable for several of these cases to stick a barrier();
> > in front and after it to be honest; that makes it more explicit that
> > these are deliberate compiler barriers rather than "actual" memory
> > access...
> >
> >   
> 
> I suppose, though I would be inclined to put the barriers in the
> wrmsr macro itself to act as documentation. 


yeah I meant like this:

static inline void native_write_msr(unsigned int msr,
 				    unsigned low, unsigned high)
{
	barrier();
	asm volatile("wrmsr" : : "c" (msr), "a"(low), "d" (high));
	barrier();
}

or in the same in the thing that calls this.

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