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Re: [Xen-devel] Re: how to enable shadow page table? Do I have to run HV

To: Long Wang <longwang@xxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: how to enable shadow page table? Do I have to run HVM guest systems for shadow paging mode?
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 16 Mar 2009 10:06:26 -0700
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>
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Long Wang wrote:
I looked into the live migration code in Xen. I need more than the mechanism
provided in live migration, as described below:

1. scan the states of all the memory pages of a domain, set dirty pages as
read-only, and clear all dirty bits for all the memory pages (so read-only
and dirty are two different bits). This procedure is done periodically.

2. When a readonly page is to be updated by the domain, the update is
trapped into the hypervisor, when I copy the page content to another place,
and set the page as writable (this page is not a page table page), makes the
update.

I find that the mechanism used in live migration cannot handle these. How
can I enable shadow paging in PV? If not, do I have to find a machine with
vmx-featured processor and run HVM for this machine?

Well, that's an option. But if you're going to be hacking Xen anyway, then it sounds like log-dirty is close to what you want. But Tim is probably the person to ask about that.

   J

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