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RE: [Xen-devel] More page-table questions.

To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, "PUCCETTI Armand" <armand.puccetti@xxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] More page-table questions.
From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Date: Mon, 12 Mar 2007 17:35:12 +0100
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Thread-topic: [Xen-devel] More page-table questions.

> -----Original Message-----
> From: Keir Fraser [mailto:keir@xxxxxxxxxxxxx] 
> Sent: 12 March 2007 16:32
> To: Petersson, Mats; Keir Fraser; PUCCETTI Armand; 
> xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] More page-table questions.
> On 12/3/07 16:26, "Petersson, Mats" <Mats.Petersson@xxxxxxx> wrote:
> > Are the page-tables ever updated directly by the guest, or is it all
> > done via hyper-calls?
> Leaf PTEs (i.e., really just PTEs, not PDEs) can be directly 
> written from
> the point-of-view of the guest. In fact they are trapped and 
> emulated by
> Xen. The guest is somewhat aware of this because it has explicitly
> write-protected all its pagetables, so if it were to attempt 
> the direct
> write on native hardware in these circumstances it would 
> receive a page
> fault.

So in one way or another, the hypervisor knows about every write to the
page-table, yes?

>  -- Keir

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