Re: [PATCH net-next v8] virtio_net: Support RX hash XDP hint

[Liang Chen]

On Tue, Apr 16, 2024 at 3:35 PM Heng Qi <hengqi@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> 在 2024/4/16 下午2:19, 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.
> >
> > 1.
> > https://lore.kernel.org/all/20231015141644.260646-1-akihiko.odaki@xxxxxxxxxx/#r
> >
> > Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>
> > ---
> >    Changes from v7:
> > - use table lookup for rss hash type
> >    Changes from v6:
> > - fix a coding style issue
> >    Changes from v5:
> > - Preservation of the hash value has been dropped, following the conclusion
> >    from discussions in V3 reviews. The virtio_net driver doesn't
> >    accessing/using the virtio_net_hdr after the XDP program execution, so
> >    nothing tragic should happen. As to the xdp program, if it smashes the
> >    entry in virtio header, it is likely buggy anyways. Additionally, looking
> >    up the Intel IGC driver,  it also does not bother with this particular
> >    aspect.
> > ---
> >   drivers/net/virtio_net.c        | 42 +++++++++++++++++++++++++++++++++
> >   include/uapi/linux/virtio_net.h |  1 +
> >   2 files changed, 43 insertions(+)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index c22d1118a133..1d750009f615 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -4621,6 +4621,47 @@ static void virtnet_set_big_packets(struct virtnet_info *vi, const int mtu)
> >       }
> >   }
> >
> > +static enum xdp_rss_hash_type
> > +virtnet_xdp_rss_type[VIRTIO_NET_HASH_REPORT_MAX_TABLE] = {
> > +     [VIRTIO_NET_HASH_REPORT_NONE] = XDP_RSS_TYPE_NONE,
> > +     [VIRTIO_NET_HASH_REPORT_IPv4] = XDP_RSS_TYPE_L3_IPV4,
> > +     [VIRTIO_NET_HASH_REPORT_TCPv4] = XDP_RSS_TYPE_L4_IPV4_TCP,
> > +     [VIRTIO_NET_HASH_REPORT_UDPv4] = XDP_RSS_TYPE_L4_IPV4_UDP,
> > +     [VIRTIO_NET_HASH_REPORT_IPv6] = XDP_RSS_TYPE_L3_IPV6,
> > +     [VIRTIO_NET_HASH_REPORT_TCPv6] = XDP_RSS_TYPE_L4_IPV6_TCP,
> > +     [VIRTIO_NET_HASH_REPORT_UDPv6] = XDP_RSS_TYPE_L4_IPV6_UDP,
> > +     [VIRTIO_NET_HASH_REPORT_IPv6_EX] = XDP_RSS_TYPE_L3_IPV6_EX,
> > +     [VIRTIO_NET_HASH_REPORT_TCPv6_EX] = XDP_RSS_TYPE_L4_IPV6_TCP_EX,
> > +     [VIRTIO_NET_HASH_REPORT_UDPv6_EX] = XDP_RSS_TYPE_L4_IPV6_UDP_EX
> > +};
> > +
> > +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;
> > +     u16 hash_report;
> > +
> > +     if (!(xdp->rxq->dev->features & NETIF_F_RXHASH))
> > +             return -ENODATA;
> > +
> > +     vi = netdev_priv(xdp->rxq->dev);
> > +     hdr_hash = (struct virtio_net_hdr_v1_hash *)(xdp->data - vi->hdr_len);
> > +     hash_report = __le16_to_cpu(hdr_hash->hash_report);
> > +
> > +     if (hash_report >= VIRTIO_NET_HASH_REPORT_MAX_TABLE)
> > +             hash_report = VIRTIO_NET_HASH_REPORT_NONE;
>
> When this happens, it may mean an error or user modification of the
> header occurred.
> Should the following *hash* value be cleared to 0?
>

Referring to the igc and mlx5 drivers, the hash value is not cleared
to 0 in such cases either. This is because if the rss type is
XDP_RSS_TYPE_NONE, the hash value is considered to be not relevant.
Thanks!

> Thanks,
> Heng
>
> > +
> > +     *rss_type = virtnet_xdp_rss_type[hash_report];
> > +     *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;
> > @@ -4747,6 +4788,7 @@ static int virtnet_probe(struct virtio_device *vdev)
> >                                 VIRTIO_NET_RSS_HASH_TYPE_UDP_EX);
> >
> >               dev->hw_features |= NETIF_F_RXHASH;
> > +             dev->xdp_metadata_ops = &virtnet_xdp_metadata_ops;
> >       }
> >
> >       if (vi->has_rss_hash_report)
> > diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> > index cc65ef0f3c3e..3ee695450096 100644
> > --- a/include/uapi/linux/virtio_net.h
> > +++ b/include/uapi/linux/virtio_net.h
> > @@ -176,6 +176,7 @@ struct virtio_net_hdr_v1_hash {
> >   #define VIRTIO_NET_HASH_REPORT_IPv6_EX         7
> >   #define VIRTIO_NET_HASH_REPORT_TCPv6_EX        8
> >   #define VIRTIO_NET_HASH_REPORT_UDPv6_EX        9
> > +#define VIRTIO_NET_HASH_REPORT_MAX_TABLE      10
> >       __le16 hash_report;
> >       __le16 padding;
> >   };
>