Commit 3d0ad09412ffe00c9afa201d01effdb6023d09b4 ("drivers/net: Disable
UFO through virtio") breaks live migration of KVM guests from older to
newer host kernels:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3d0ad09412ffe00c9afa201d01effdb6023d09b4
The problem occurs when a guest running on a host kernel without commit
3d0ad0941 in tun.ko attempts to live migration to a host with commit
3d0ad0941.
Live migration fails in QEMU with the following error message:
virtio-net: saved image requires TUN_F_UFO support
The old host tun.ko advertised support for TUN_F_UFO. The new host
tun.ko does not and that's why QEMU aborts live migration. QEMU cannot
change the features of a running virtio-net device.
tuxcrafter provided logs from two Debian hosts migrating from
3.2.60-1+deb7u3 to 3.2.63-2+deb7u1:
http://paste.debian.net/131264/
I haven't investigated enough to suggest a fix, just wanted to bring it
to your attention. Soon a lot of people will be hitting this problem as
they upgrade their infrastructure and migrate guests - seems like a
critical issue.
Stefan
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