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On Thu, Nov 6, 2025 at 6:17 AM Peter Xu <[email protected]> wrote:
>
> 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,
I see, so the reason is that the destination doesn't support USO in
the kernel. For those kinds of features that depend on the kernel, I
agree to disable them by default. But I'm not sure if it's too late or
maybe we can do strict peer feature check like this in
virtio_net_get_features():
if (!peer_has_uso(n)) {
- virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_USO);
- virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
- virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
+ if (n->strict_peer_feature_check) {
+ if (virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_USO) |
+ virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_USO4) |
+ virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_USO6))
+ error_setg(errp, "virtio_net: peer doesn't support USO");
+ } else {
+ virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_USO);
+ virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
+ virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
+ }
}
So qemu would fail earlier than fail the migration.
Thanks
>
> --
> Peter Xu
>
