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Re: [Xen-devel] Save/restore, migration of HVM-guest's

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Subject: Re: [Xen-devel] Save/restore, migration of HVM-guest's
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Wed, 26 Apr 2006 23:01:34 +0100
Cc: Thorolf Godawa <nospam@xxxxxxxxx>
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> can s.b. tell me what the actual status for save/restore and migration
> of unmodified HVM-guest's is? Are there any news since Xen 3.0.1, any
> timeframe when it could be available?

Since memory is fully virtualised a fair bit of the infrastructure necessary 
is already there.  I don't know to what extent page dirtying is exported to 
userspace for an HVM domain, which is an important part of live migration 
(although not necessary for suspend / resume).

Somebody might in principle be able to hack the Qemu device models to suspend 
their state, at which point almost all the pieces will be in place.

However, the primary plan (I believe) is to move the device emulator into a 
paravirtualised domain that runs alongside the HVM domain.  This encapsulates 
all the state of the device models in an opaque way and migration can be 
achieved by migrating the device model emulator along with the domain in 

There was recently a call for help on implementing this new model (which 
should also improve emulation performance), but I'm not sure anyone is 
working directly on it yet.  Since the emulator domain is likely to be based 
on mini-os, a number of people are working on cleaning up its code base and 
making it run on 64-bit x86.


Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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