Re: [PATCH] virtio_net: Support RX hash XDP hint

[Liang Chen]

On Mon, Jan 22, 2024 at 7:10 PM Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> wrote:
>
> Hi Liang Chen,
>
> 在 2024/1/22 下午6:22, Liang Chen 写道:
> > The RSS hash report is a feature that's part of the virtio specification.
> > Currently, virtio backends like qemu, vdpa (mlx5), and potentially vhost
> > (still a work in progress as per [1]) support this feature. While the
> > capability to obtain the RSS hash has been enabled in the normal path,
> > it's currently missing in the XDP path. Therefore, we are introducing XDP
> > hints through kfuncs to allow XDP programs to access the RSS hash.
> >
> > Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>
> > ---
> >   drivers/net/virtio_net.c | 56 ++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 56 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index d7ce4a1011ea..1463a4709e3c 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -4579,6 +4579,60 @@ static void virtnet_set_big_packets(struct virtnet_info *vi, const int mtu)
> >       }
> >   }
> >
> > +static int virtnet_xdp_rx_hash(const struct xdp_md *_ctx, u32 *hash,
> > +                        enum xdp_rss_hash_type *rss_type)
> > +{
> > +     const struct xdp_buff *xdp = (void *)_ctx;
> > +     struct virtio_net_hdr_v1_hash *hdr_hash;
> > +     struct virtnet_info *vi;
> > +
> > +     if (!(xdp->rxq->dev->features & NETIF_F_RXHASH))
>
> I think 'vi->has_rss_hash_report' should be used here.
> NETIF_F_RXHASH cannot guarantee that the hash report feature is negotiated,
> and accessing hash_report and hash_value is unsafe at this time.
>

My understanding is that rxhash in dev->features is turned on only if
the corresponding hw feature is set. We will double check on this.

> > +             return -ENODATA;
> > +
> > +     vi = netdev_priv(xdp->rxq->dev);
> > +     hdr_hash = (struct virtio_net_hdr_v1_hash *)(xdp->data - vi->hdr_len);
>
> If the virtio-net-hdr is overrided by the XDP prog, how can this be done
> correctly and as expected?
>

Yeah, thanks for bringing up this concern. We are actively working on
a fix of this issue(possibly with a wrapper structure of xdp_buff).

Thanks,
Liang

> Thanks,
> Heng
>
> > +
> > +     switch (__le16_to_cpu(hdr_hash->hash_report)) {
> > +             case VIRTIO_NET_HASH_REPORT_TCPv4:
> > +                     *rss_type = XDP_RSS_TYPE_L4_IPV4_TCP;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_UDPv4:
> > +                     *rss_type = XDP_RSS_TYPE_L4_IPV4_UDP;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_TCPv6:
> > +                     *rss_type = XDP_RSS_TYPE_L4_IPV6_TCP;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_UDPv6:
> > +                     *rss_type = XDP_RSS_TYPE_L4_IPV6_UDP;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_TCPv6_EX:
> > +                     *rss_type = XDP_RSS_TYPE_L4_IPV6_TCP_EX;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_UDPv6_EX:
> > +                     *rss_type = XDP_RSS_TYPE_L4_IPV6_UDP_EX;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_IPv4:
> > +                     *rss_type = XDP_RSS_TYPE_L3_IPV4;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_IPv6:
> > +                     *rss_type = XDP_RSS_TYPE_L3_IPV6;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_IPv6_EX:
> > +                     *rss_type = XDP_RSS_TYPE_L3_IPV6_EX;
> > +                     break;
> > +             case VIRTIO_NET_HASH_REPORT_NONE:
> > +             default:
> > +                     *rss_type = XDP_RSS_TYPE_NONE;
> > +     }
> > +
> > +     *hash = __le32_to_cpu(hdr_hash->hash_value);
> > +     return 0;
> > +}
> > +
> > +static const struct xdp_metadata_ops virtnet_xdp_metadata_ops = {
> > +     .xmo_rx_hash                    = virtnet_xdp_rx_hash,
> > +};
> > +
> >   static int virtnet_probe(struct virtio_device *vdev)
> >   {
> >       int i, err = -ENOMEM;
> > @@ -4613,6 +4667,8 @@ static int virtnet_probe(struct virtio_device *vdev)
> >       dev->ethtool_ops = &virtnet_ethtool_ops;
> >       SET_NETDEV_DEV(dev, &vdev->dev);
> >
> > +     dev->xdp_metadata_ops = &virtnet_xdp_metadata_ops;
> > +
> >       /* Do we support "hardware" checksums? */
> >       if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
> >               /* This opens up the world of extra features. */
>