On Tue, Mar 17, 2026 at 07:34:33PM +0800, Di Zhu wrote:
> Negotiating VIRTIO_NET_F_CTRL_GUEST_OFFLOADS indicates the device
> allows control over offload support, but the offloads that can be
> controlled may have nothing to do with GRO (e.g., if neither GUEST_TSO4
> nor GUEST_TSO6 is supported).
>
> In such a setup, reporting NETIF_F_GRO_HW as available for the device
> is too optimistic and misleading to the user.
>
> Improve the situation by masking off NETIF_F_GRO_HW unless the device
> possesses actual GRO-related offload capabilities. Out of an abundance
> of caution, this does not change the current behaviour for hardware with
> just v6 or just v4 GRO: current interfaces do not allow distinguishing
> between v6/v4 GRO, so we can't expose them to userspace precisely.
>
> Fixes: dbcf24d15388 ("virtio-net: use NETIF_F_GRO_HW instead of NETIF_F_LRO")
> Signed-off-by: Di Zhu <[email protected]>
> ---
> /* v3 */
> -Update Fixes tag to dbcf24d15388
> -Refine commit message using Maintainer's "too optimistic"
> phrasing to clarify the risk of misleading configurations.
>
> /* 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;
> +
Hmm wait a second. Isn't this late? netdev registered, even link is
up already.
Documentation/networking/netdev-features.rst says:
1. netdev->hw_features set contains features whose state may possibly
be changed (enabled or disabled) for a particular device by user's
request. This set should be initialized in ndo_init callback and not
changed later.
I'd say let's move it up?
Having said that, we already have a bug:
dev->hw_features &= ~NETIF_F_RXHASH;
is after register, too.
This is because we take pains to recover from these commands failing.
Except, we completely ignore that in virtnet_set_rxfh ...
Cc relevant contributors to maybe take a look at fixing all that.
> rtnl_unlock();
>
> err = virtnet_cpu_notif_add(vi);
> --
> 2.34.1
>
