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Re: [Xen-devel] write page table in user mode

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, "Su, Disheng" <disheng.su@xxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] write page table in user mode
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 02 Feb 2008 15:15:58 +0000
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On 2/2/08 14:08, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Maybe we can disable such heuristics only when observing guest
> clear CR0.wp actively? Or later out-of-sync can also help here.
> BTW, it's worthy of adding a seperate perfc counter for user-level
> access caused unshadow. :-)

Yes, and if we can do better at working out when pages should be unshadowed,
we can then perhaps get rid of the unshadow-on-user-access heuristic.

Presumably things still work though? The page will simply get re-shadowed on
next use. I suppose the guest will crash if the shadow code is unable to
unshadow the page though (e.g., because it is current base page directory).
Perhaps we should emulate the access anyway if the page cannot be

 -- Keir

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