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Re: [Xen-devel] read-only pagetable entries

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] read-only pagetable entries
From: Srujan Kotikela <ksrujandas@xxxxxxxxx>
Date: Mon, 20 Jun 2011 07:33:02 -0500
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Clicked reply instead of reply-to-all.

Srujan D. Kotikela

On Mon, Jun 20, 2011 at 7:10 AM, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:

Please don't take discussions off-list.  Cc'ing xen-devel again.

At 12:58 +0100 on 20 Jun (1308574721), Srujan Kotikela wrote:
> Hi,
> Thanks for the prompt reply. Can you tell me how to achieve the same
> in PV guests?

In PV guests you could try turning on shadow paging and enforcing the same
read-only idea (but PV guests don't have a p2m table so that will be
messy; you might be able to hook gmfn_to_mfn?).  Or you could update the
PV pagetable interface to require the guest to make the PTE read-only
(by hooking adjust_guest_l1e or similar).  That would have much better
performance but might need changes to the guest kernel to cope with its
PTEs being read-only.

> Also is there any standard/official documentation for
> Xen's memory management?

Not really, no.  The basic ideas are laid out in the original Xen papers
and in some of the Xen books that have been published but there's no
technical documentation for the code except what's in comments and HG
log entries.


Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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