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[libvirt-users] live migration causes guest system to crash when accessing the network

Hi all,

we've been using libvirt/KVM ever since it was included in Ubuntu 10.04 LTS. At first, it wasn't possible to do live block migrations. We got used to that.

And now block migration has been possible since Ubuntu 12.04 LTS. And we're excited.

There's just one hitch:

Many of migrations have the result that the system is successfully migrated, but will no longer run. Sometimes, it still runs but can't access the network. Sometimes it just freezes completely, and doesn't even show a kernel panic on the console. And sometimes the network still works but will crash when sending ICMP messages from within the guest. And every once in a while the guest system will continue to run.

Most of our guests use virtio for both networking and storage. The guest OS's are mostly Ubuntu 12.04, but also one 11.04 and several 10.04's. A few older ones are still around, as well. The older ones don't support virtio though, so here we use the emulated intel e1000 network card and IDE storage. The guests are connected to a common bridge on the node, which provides access to the outside network. There is no NAT.

Oh, and I read that different CPU capabilities (flags, etc.) can cause live migrations to fail. So I used the recommended procedure to determine the least common denominator of the CPUs on our nodes and configured all the guests to use only those CPU capabilities. After a restart, I verified that the kernel correctly identified the configured CPU type and flags.

Does anyone have an idea how I can go about debugging the issue? Or has anyone experienced this issue and found a solution?

*Sebastian J. Bronner*

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