Re: [RFC PATCH] virtio-net: introduce strict peer feature check

[Jason Wang <jasowang@redhat.com>]

On Thu, Nov 13, 2025 at 5:55 AM Peter Xu <peterx@redhat.com> wrote:
>
> On Fri, Nov 07, 2025 at 10:01:49AM +0800, Jason Wang wrote:
> > We used to clear features silently in virtio_net_get_features() even
> > if it is required. This complicates the live migration compatibility
> > as the management layer may think the feature is enabled but in fact
> > not.
> >
> > Let's add a strict feature check to make sure if there's a mismatch
> > between the required feature and peer, fail the get_features()
> > immediately instead of waiting until the migration to fail. This
> > offload the migration compatibility completely to the management
> > layer.
> >
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
>
> Jason, thanks for help looking into the problem!
>
> Am I right that after this patch applied, whenever a new QEMU boots with
> the new machine types (e.g. having USO* by default ON), will fail to boot
> on an old kernel that doesn't support USO*, but ask the users to turn off
> USO* features explicitly in the virtio-net devices?
>
> Thanks,

Yes, I wonder if this can help in dealing with migration compatibility issues.

Thanks