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

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Message-ID: <4862D247.2010709@kernel.org>
Date:	Wed, 25 Jun 2008 16:18:31 -0700
From:	"H. Peter Anvin" <hpa@...nel.org>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>, 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

Arjan van de Ven wrote:
>>>   
>> 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.
> 

Actually, I believe the barrier(); before is actually incorrect, since 
it would affect the wrmsr() register arguments rather than the wrmsr 
instruction itself.

	-hpa
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