> Thanks! Yes something to improve:
>
> On Mon, Mar 16, 2026 at 03:21:52PM +0800, Di Zhu wrote:
> > Although VIRTIO_NET_F_CTRL_GUEST_OFFLOADS is negotiated, which
> > indicates the device supports dynamic control of guest offloads, it
> > does not necessarily mean the device supports specific hardware GRO
> > features.
> >
> > If none of the features defined in GUEST_OFFLOAD_GRO_HW_MASK (such as
> > TSO4, TSO6, or UFO) are present in vi->guest_offloads_capable, the
> > device effectively lacks the hardware capability to perform GRO.
>
> So what is the user-visible problem this is trying to address?
A key concern is that once a user enables NETIF_F_GRO_HW via ethtool,
they might manually disable software GRO (ethtool -K eth0 gro off) assuming the
hardware is now handling the aggregation.
Secondly, while we haven't encountered a specific hardware failure yet,
enabling a hardware offload feature that the DPU does not physically support
introduces the risk of undefined hardware behavior
> >
> > So, making NETIF_F_GRO_HW conditional on these feature bits ensures
> > the stack does not enable an unsupported hardware offload configuration.
>
> I guess the assumption is that without this, something enables such a config?
> Which
> stack is this and what happens then?
>
Sorry for the confusion, let me clarify the intent.
The 'stack' here refers to the ethtool interface and the netset (ioctl/netlink)
path.
>
> > Fixes: a02e8964eaf9 ("virtio-net: ethtool configurable LRO")
> > Signed-off-by: Di Zhu <[email protected]>
>
> judging by this, has something to do with LRO?
>
> > ---
> > /* v2 */
> > -make the modified logic clearer
> > ---
> > drivers/net/virtio_net.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
> > 72d6a9c6a5a2..b233c99925e9 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -6781,8 +6781,6 @@ static int virtnet_probe(struct virtio_device *vdev)
> > if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> > virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO6))
> > dev->features |= NETIF_F_GRO_HW;
> > - if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS))
> > - dev->hw_features |= NETIF_F_GRO_HW;
> >
> > dev->vlan_features = dev->features;
> > dev->xdp_features = NETDEV_XDP_ACT_BASIC |
> NETDEV_XDP_ACT_REDIRECT |
> > @@ -7058,6 +7056,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> > }
> > vi->guest_offloads_capable = vi->guest_offloads;
> >
> > + if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) &&
> > + (vi->guest_offloads_capable & GUEST_OFFLOAD_GRO_HW_MASK))
> > + dev->hw_features |= NETIF_F_GRO_HW;
> > +
> > rtnl_unlock();
> >
> > err = virtnet_cpu_notif_add(vi);
> > --
> > 2.34.1
> >
>
