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Re: [Xen-devel] Re: how to enable shadow page table? Do I havetorun HVM

To: Long Wang <longwang@xxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: how to enable shadow page table? Do I havetorun HVM guest systems for shadow paging mode?
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Thu, 19 Mar 2009 16:16:21 +0000
Cc: 'Jeremy Fitzhardinge' <jeremy@xxxxxxxx>, 'Xen-devel' <xen-devel@xxxxxxxxxxxxxxxxxxx>
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At 15:55 +0000 on 19 Mar (1237478115), Long Wang wrote:
> I am a little confused. You wrote: 
> 1) "The dirty bit of a *shadow* PTE is usually set by _sh_propagate (since
> we don't care about it) except for some optimizations to do with HVM video
> RAM mappings, where it's set by the MMU." 
> 2) "Only for the *shadow* PTE, since that's the only one the MMU ever
> Sees". 
> Do you mean that most of *shadow* PTE dirty bits (in PV) are set by
> _sh_propagate() (through a read-only-bit-triggered interception)?

No, I mean that when _sh_propagate() makes a shadow PTE that has the R/W
bit set, it usually sets the Dirty bit as well (to save the MMU the
extra write cycle later).



Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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