Re: [Xen-devel] migration regression in xen-4.11 and qemu-2.11 and qcow2

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 10 May 2018, Olaf Hering wrote:
> Am Wed, 9 May 2018 14:43:17 -0700 (PDT)
> schrieb Stefano Stabellini <sstabellini@xxxxxxxxxx>:
> 
> > 512b109ec962 is a very old commit: why is it causing problems to Xen
> > 4.10 and Xen 4.11 HVM migration? What is the error exactly? Sorry, I
> > might be missing some context.
> 
> It is papering over the real issue, thats why one can still migrate a
> pvops HVM domU with current toolstack. Upstream kernel simply does the
> work that is supposed to be done by qemu itself. Since the xenlinux based
> kernel does not do that work (it never had a need to do the unplug twice),
> migration fails.
> 
> qemu has to carry the unplug state from one dom0 to another dom0 during
> migration, simply because unplug is a one-time operation that can not 
> be undone. I wonder how to do that, if qemu already has code to carry its
> state.

You could add a property to vmstate_xen_platform of xen_platform.c, but
you need to pay attention to legacy compatibility. Inevitably, there
will be older versions that do not have the new vmstate_xen_platform
field or do not set it properly.

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