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Re: [Xen-devel] Shadow Page Tables in Xen

To: Gianluca Guida <glguida@xxxxxxxxx>
Subject: Re: [Xen-devel] Shadow Page Tables in Xen
From: priya sehgal <priyagps@xxxxxxxxxxx>
Date: Fri, 24 Apr 2009 10:03:26 +0530 (IST)
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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> Ok that seems, but please note that at the moment shadows
> always set the DIRTY bit (unless we're tracking a VRAM
> address), so you might have to set the dirty bit clean when
> propagating the shadow, which is a bit too intrusive
> perhaps. But yes, that would work.

I see one problem, which we might introduce by making the SPTE entries of
all the pages in the group RW, but not marking their corresponding GPTE entry 
as DIRTY -- if the Guest writes to a page (marked as RW in SPTE) and makes it 
dirty, there is no way Hypervisor will know about it, and so it cannot mark 
GPTE's entry as DIRTY. This might lead to inconsistency between the shadow and 
guest page tables. Also, the OS running inside the guest will not see correct 
picture about the dirty pages, thereby not flushing the dirty pages.

Please let me know if I am right about the problem created due to our proposed 



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