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

[Xuan Zhuo]

On Wed, 24 Jan 2024 10:04:51 +0800, Liang Chen <liangchen.linux@xxxxxxxxx> wrote:
> 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).

Are there some places to save the hash before run xdp?

Thanks.


>
> 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. */
> >
>