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Re: [Qemu-devel] migrating instances from qemu-kvm to qemu

From: Paolo Bonzini
Subject: Re: [Qemu-devel] migrating instances from qemu-kvm to qemu
Date: Wed, 19 Mar 2014 16:49:53 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

Il 19/03/2014 16:42, Serge E. Hallyn ha scritto:

at https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1291321
it was found that migrating running vms from a machine with
qemu-kvm to one with qemu, migration fails due to some mismatches.
The first one we usually hit is

Length mismatch: vga.vram: 1000000 in != 800000

while the second one is network card (and I have not gone beyond

This is just a different default. Make sure you specify the right model on the command line.

The vga one can be handled on the command line by
specifying the -global cirrus-vga.vrammem_mb=8.  However that
doesn't help with a libvirt migration.

You can patch Ubuntu's QEMU to detect old machine types (pc-1.2 and earlier) and give cirrus-vga 16MB memory by default. Migration only works with versioned machine types (or between same-version QEMU), so it's okay to only do it there.

I guess this happens at ram_load() unfortunately - is there any
good way that this could be detected at incoming migration time
and the virtual hardware modified as needed for migration to

It cannot, but the destination can be patched to operate correctly for the old machine types, on the assumption that migration from the old machine types is always from Ubuntu's qemu-kvm.


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