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We recently added iSCSI storage to two Xen servers running a mix of Gentoo and Ubuntu 10.04 and 12.04 domUs. When trying out live migration of domU I found that I can migrate just fine the Ubuntu ones (both flavours) but not the Gentoo ones.

The latter run our own kernels, with a kernel config born in the 2.6.18 era and ported on from release to release, now running Linux 3.10.7. They're stripped down configurations tuned for domU usage (eg. no PCI or other hardware support, no modules, etc...).

When trying to migrate one, xm migrate seems to succeed, on the destination node I can see the domU in running state (and consuming CPU time), but it can't talk to the outside world (no packets in/out the vif, no I/O on the block device, no activity on xm console even if it can attach just fine.

I suspect there's some kernel config parameters I'm missing or that I got wrong and that's preventing live migration... did a lot of googling and searched Xen documentation & wiki, without luck.

What are the exact requirements on a recent (3.x, pvops) Linux kernel to be used as domU and be able to migrate?

EDIT: as I expected, the Gentoo domains will give the exact same problems when doing an xm save; xm restore on the same node.

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After some testing with various kernel configuration, I nailed it to CONFIG_SMP.

That, or one of its dependencies, is required to allow Xen domU kernels to be saved and restored... and thus also migrated from host to host.

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