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Re: [Xen-devel] [PATCH] Do not set page's count_info directly

To: Gianluca Guida <glguida@xxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Do not set page's count_info directly
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 05 Mar 2009 12:45:58 +0000
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, Gianluca Guida <Gianluca.Guida@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 05/03/2009 12:32, "Gianluca Guida" <glguida@xxxxxxxxx> wrote:

>> Also currently shadow code assume count_info is 0 for shadow page, however,
>> this is invalid after the new flags. Change some assert in shadow code.
> 
> Yes, that's correct. I find, though, (count_info & PGC_count_mask !=
> 0) as a check if the page is a shadow *very* confusing. Could you
> define a macro with something like page_is_a_shadow_page() and hide
> this mm.c dirty secret?

This would be a shadow-code-specific macro. In general count_mask==0 can
also mean the page is free, for example.

 -- Keir



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