linux-kernel - Re: Folding _PAGE_PWT into _PAGE_PCD (was Re: unify pagetable accessors patch causes double fault II)

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Date:	Tue, 15 Jan 2008 09:32:53 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: Folding _PAGE_PWT into _PAGE_PCD (was Re: unify pagetable accessors
 patch causes double fault II)

Andi Kleen wrote:
>> BTW, I just noticed that _PAGE_PWT has been folded into _PAGE_PCD.  This 
>> seems like a really bad idea to me, since it breaks the rule that 
>> _PAGE_X == 1 << _PAGE_BIT_X.  I can't think of a specific place where 
>> this would cause problems, but this kind of non-uniformity always ends 
>> up biting someone in the arse.
>>     
>
> Agreed that it's a bad idea.
>
>   
>> I think having a specific _PAGE_NOCACHE which combines these bits is a 
>> better approach.
>>     
>
> CPA series adds that already
>
> +/* Needs special handling for large pages */
> +#define _PAGE_CACHE     (_PAGE_PCD|_PAGE_PWT|_PAGE_PAT)
>   

Good, but isn't the name _PAGE_CACHE misleading?  Or does it mean 
something else in the context of PAT?

    J
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