From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: Re: [PATCH]Add a flag for shadow pages
Date: Wed, 04 Mar 2009 13:19:17 +0000
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To: Tim Deegan <Tim.Deegan@eu.citrix.com>
Cc: Gianluca Guida <Gianluca.Guida@eu.citrix.com>, "Jiang,
	Yunhong" <yunhong.jiang@intel.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
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On 04/03/2009 12:13, "Tim Deegan" <Tim.Deegan@eu.citrix.com> wrote:

> shadow_get_page_from_l1e() should never be handling a pointer to a
> shadow -- if it does that then we've let the guest see the shadows and
> all invariants go out the window.
> 
> sh_mfn_is_a_pagetable() looks OK too; it only gets called based on the
> contents of shadow PTEs or the MFNs that guests are writing to, both of
> which should be safe.
> 
> It all feels a bit fragile to me though, compared to the old layout
> where we always knew the owner field would be NULL.

This is the tradeoff for the new get_page() implementation and wider
reference counts. We just need to be careful and use
page_get_owner_and_reference() in the few cases it seems to be needed.

 -- Keir