linux-kernel - Re: [PATCH] virtio_net: Support RX hash XDP hint

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Date: Wed, 24 Jan 2024 10:12:43 +0800
From: Jason Wang <jasowang@...hat.com>
To: Liang Chen <liangchen.linux@...il.com>
Cc: mst@...hat.com, virtualization@...ts.linux-foundation.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio_net: Support RX hash XDP hint

On Mon, Jan 22, 2024 at 6:23 PM Liang Chen <liangchen.linux@...il.com> wrote:
>
> 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@...il.com>
> ---
>  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))
> +               return -ENODATA;
> +
> +       vi = netdev_priv(xdp->rxq->dev);
> +       hdr_hash = (struct virtio_net_hdr_v1_hash *)(xdp->data - vi->hdr_len);

Is there a guarantee that the hdr is not modified?

Thanks