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Date:	Tue, 02 Oct 2007 23:18:22 -0700
From:	"H. Peter Anvin" <>
To:	Nick Piggin <>
CC:	Chuck Ebbert <>,
	Arjan van de Ven <>,
	Kirill Korotaev <>,
	Andrew Morton <>, Andi Kleen <>,
	Linux Kernel Mailing List <>,
Subject: Re: [PATCH] mark read_crX() asm code as volatile

Nick Piggin wrote:
>> This should work because the result gets used before reading again:
>> read_cr3(a);
>> write_cr3(a | 1);
>> read_cr3(a);
>> But this might be reordered so that b gets read before the write:
>> read_cr3(a);
>> write_cr3(a | 1);
>> read_cr3(b);
>> ?
> I don't see how, as write_cr3 clobbers memory.

Because read_cr3() doesn't depend on memory, and b could be stored in a 

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