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References: <20160218113211.9760.85475.stgit@bahia.huguette.org>
From: Laurent Vivier <lvivier@redhat.com>
Message-ID: <56C72986.2030205@redhat.com>
Date: Fri, 19 Feb 2016 15:41:10 +0100
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Subject: Re: [Qemu-devel] [PATCH v3 0/2] Fix migration of old pseries
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To: Greg Kurz <gkurz@linux.vnet.ibm.com>, Juan Quintela <quintela@redhat.com>
Cc: Amit Shah <amit.shah@redhat.com>, David Gibson <david@gibson.dropbear.id.au>, qemu-ppc@nongnu.org, qemu-devel@nongnu.org, "Dr. David Alan Gilbert" <dgilbert@redhat.com>



On 18/02/2016 12:32, Greg Kurz wrote:
> QEMU 2.4 broke the migration of old pseries machine with the addition
> of configuration sections, which are sent unconditionally.
> 
> We assume that QEMU 2.3 is more deployed than any newer release (based on
> the versions currently shipped by most distros). This v3 series hence
> reverses the logic from v2: it now fully fixes migration of old pseries
> from/to QEMU 2.3 and provides a manual workaround for the QEMU 2.4/2.4.1/2.5
> case.
> 
> With this series, I could migrate the same pseries-2.3 instance in a full
> 2.3->2.6->2.5->2.6->2.4->2.6->2.3 cycle.

I've tested all possible combinations, with and without these patches.
The result is here:

http://wiki.qemu.org/Migration/Compatibility/pseries

- Migration is totally broken in qemu-2.2
- without these patches, migration cannot be done from/to qemu-2.3
- with these patches, qemu-2.3 can migrate to/from qemu-2.6
- 1st patch breaks pseries-2.2, pseries-2.3 migration from/to
  qemu-2.4/2.5 but 2nd patch allows to fix this manually.

Feel free to update the page.

Laurent