linux-kernel - Re: [PATCH] x86: fix ordering constraints on crX read/writes

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Message-ID: <4C3EB3C7.90108@redhat.com>
Date:	Thu, 15 Jul 2010 10:07:51 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Glauber Costa <glommer@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: fix ordering constraints on crX read/writes

On 07/15/2010 03:28 AM, Zachary Amsden wrote:
>>   static inline void native_write_cr2(unsigned long val)
>>   {
>> -    asm volatile("mov %0,%%cr2": : "r" (val), "m" (__force_order));
>> +    asm volatile("mov %1,%%cr2": "+m" (__force_order) : "r" (val) : 
>> "memory");
>>   }
>
>
> You don't need the memory clobber there.  Technically, this should 
> never be used, however.

kvm writes cr2 in order to present the correct value to the guest.  It 
doesn't use native_write_cr2(), however.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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