Re: [BUG] Migration failure between QEMU 9.2.4 → 8.2.10 due to virtio-net feature mismatch (VIRTIO_F_RING_RESET / USO features)

[Peter Xu <peterx@redhat.com>]

On Wed, Nov 05, 2025 at 10:27:59AM +0100, Jinpu Wang wrote:
> > > These are not present (or not supported) on QEMU 8.2.10, which causes
> > > the migration state load to fail.
> >
> > Interesting, we've already done the compat work:
> >
> > GlobalProperty hw_compat_8_1[] = {
> >     { TYPE_PCI_BRIDGE, "x-pci-express-writeable-slt-bug", "true" },
> >     { "ramfb", "x-migrate", "off" },
> >     { "vfio-pci-nohotplug", "x-ramfb-migrate", "off" },
> >     { "igb", "x-pcie-flr-init", "off" },
> >     { TYPE_VIRTIO_NET, "host_uso", "off"},
> >     { TYPE_VIRTIO_NET, "guest_uso4", "off"},
> >     { TYPE_VIRTIO_NET, "guest_uso6", "off"},
> > };
> > const size_t hw_compat_8_1_len = G_N_ELEMENTS(hw_compat_8_1);
> Yeah, I noticed the same.

AFAICT, this is a known issue..

Thomas and I used to suggest we should not turn on USO* by default by
probing kernel, but only allow user choosing it explicitly in a VM
setup. IOW, dest qemu should stop booting at all when kernel is too old
(when user chose the feature).

See:

https://lore.kernel.org/all/ZqQNKZ9_OPhDq2AK@x1n/

Thanks,

-- 
Peter Xu