linux-kernel - Re: [PATCH 1/6] x86: fix NX bit handling in change_page

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Date:	Fri, 25 Jan 2008 12:05:10 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"Huang, Ying" <ying.huang@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] x86: fix NX bit handling in change_page_attr

Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
>
>   
>> ...
>> +       ref_prot = pte_pgprot(pte_mkexec(pte_clrhuge(*kpte)));
>>
>> i.e. it now goes through all the proper accessors.
>>     
>
> i guess it would be nicer to have the proper accessors to just clear the 
> NX bit from ref-prot - instead of re-constructing the *kpte from 
> scratch. But i see no other way to do it right now than to access 
> pgprot_val() as an lvalue. Jeremy, what would be the best approach here?

The pte_* accessors are really just helpers, so they're not mandatory.  
Something like this would be fine:

	refprot = __pgprot(pgprot_val(refprot) & ~_PAGE_NX);

This is identical to the lvalue form, but avoids using it as an lvalue.

    J
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