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Re: [Xen-devel] Tracking guest pages modified by qemu-dm / backend

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] Tracking guest pages modified by qemu-dm / backend
From: AP <apxeng@xxxxxxxxx>
Date: Thu, 23 Jun 2011 11:06:28 -0700
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On Wed, Jun 22, 2011 at 1:49 AM, Tim Deegan <Tim.Deegan@xxxxxxxxxx> wrote:
> Hi,
> At 15:43 -0700 on 21 Jun (1308671006), AP wrote:
>> Consider an HVM domain with EPT. When qemu-dm, backend or any other
>> device model modifies DomU memory (like on a disk read or packet
>> received), how does Xen track the pages that have been modified? For
>> example, when an DomU is being migrated while IO is occurring.
> Backends use grant tables to map guest memory; the granted pages are
> marked dirty when the backend disconnects.  Qemu-dm uses the
> HVMOP_modified memory hypercall to tell Xen that it's written to
> the guest's memory.

>From what I see for EPT/HAP, log dirty is turned on only during domain
save. Is that true or am I missing something. Plus how does dirty
tracking occur with EPT since those tables don't have a dirty bit? Is
it using the log_dirty_bitmap?


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