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

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, Gianluca Guida <glguida@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 14:50:49 +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 14:33, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

>> This would be a shadow-code-specific macro. In general count_mask==0 can
>> also mean the page is free, for example.
> 
> Maybe I'm wrong, but anonymous page will have count_mask==0 while they are
> allocated.
> 
> Currently the only way that we can make sure the guest is free is through the
> boot allocator bitmap. When the bit is clear, the page is free.
> When the bit is set, and the count_mask!=0, then it is owned by someone like
> guest ram, p2m table etc. if the count_mask==0, then it is either a shadow
> page or a anoynymous page.
> 
> Or do I missed anything?

You are correct. I only gave one obvious example where count_info==0.

 -- Keir



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