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 <4ada64aa-87ec-4340-9892-be52c1f27a97@linux.alibaba.com> <CAKhg4t+ayD-MPK8FwZFURZyX32d8gk26GdytwRiRjJBwBbaR6w@mail.gmail.com>
 <1706076301.4647658-1-xuanzhuo@linux.alibaba.com>
In-Reply-To: <1706076301.4647658-1-xuanzhuo@linux.alibaba.com>
From: Liang Chen <liangchen.linux@gmail.com>
Date: Wed, 24 Jan 2024 16:04:47 +0800
Message-ID: <CAKhg4tJd7=xpj895RzEQSADfH_eVhDYesCOk_iXz_8RMRWzjHA@mail.gmail.com>
Subject: Re: [PATCH] virtio_net: Support RX hash XDP hint
To: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: mst@redhat.com, jasowang@redhat.com, 
	virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, 
	Heng Qi <hengqi@linux.alibaba.com>
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On Wed, Jan 24, 2024 at 2:06=E2=80=AFPM Xuan Zhuo <xuanzhuo@linux.alibaba.c=
om> wrote:
>
> On Wed, 24 Jan 2024 10:04:51 +0800, Liang Chen <liangchen.linux@gmail.com=
> wrote:
> > On Mon, Jan 22, 2024 at 7:10=E2=80=AFPM Heng Qi <hengqi@linux.alibaba.c=
om> wrote:
> > >
> > > Hi Liang Chen,
> > >
> > > =E5=9C=A8 2024/1/22 =E4=B8=8B=E5=8D=886:22, Liang Chen =E5=86=99=E9=
=81=93:
> > > > The RSS hash report is a feature that's part of the virtio specific=
ation.
> > > > Currently, virtio backends like qemu, vdpa (mlx5), and potentially =
vhost
> > > > (still a work in progress as per [1]) support this feature. While t=
he
> > > > capability to obtain the RSS hash has been enabled in the normal pa=
th,
> > > > it's currently missing in the XDP path. Therefore, we are introduci=
ng XDP
> > > > hints through kfuncs to allow XDP programs to access the RSS hash.
> > > >
> > > > Signed-off-by: Liang Chen <liangchen.linux@gmail.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 v=
irtnet_info *vi, const int mtu)
> > > >       }
> > > >   }
> > > >
> > > > +static int virtnet_xdp_rx_hash(const struct xdp_md *_ctx, u32 *has=
h,
> > > > +                        enum xdp_rss_hash_type *rss_type)
> > > > +{
> > > > +     const struct xdp_buff *xdp =3D (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 negot=
iated,
> > > 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 =3D netdev_priv(xdp->rxq->dev);
> > > > +     hdr_hash =3D (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 d=
one
> > > 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?
>

Yeah, it will be saved in a wrapper structure. Thanks.

> Thanks.
>
>
> >
> > Thanks,
> > Liang
> >
> > > Thanks,
> > > Heng
> > >
> > > > +
> > > > +     switch (__le16_to_cpu(hdr_hash->hash_report)) {
> > > > +             case VIRTIO_NET_HASH_REPORT_TCPv4:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L4_IPV4_TCP;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_UDPv4:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L4_IPV4_UDP;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_TCPv6:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L4_IPV6_TCP;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_UDPv6:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L4_IPV6_UDP;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_TCPv6_EX:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L4_IPV6_TCP_EX;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_UDPv6_EX:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L4_IPV6_UDP_EX;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_IPv4:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L3_IPV4;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_IPv6:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L3_IPV6;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_IPv6_EX:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_L3_IPV6_EX;
> > > > +                     break;
> > > > +             case VIRTIO_NET_HASH_REPORT_NONE:
> > > > +             default:
> > > > +                     *rss_type =3D XDP_RSS_TYPE_NONE;
> > > > +     }
> > > > +
> > > > +     *hash =3D __le32_to_cpu(hdr_hash->hash_value);
> > > > +     return 0;
> > > > +}
> > > > +
> > > > +static const struct xdp_metadata_ops virtnet_xdp_metadata_ops =3D =
{
> > > > +     .xmo_rx_hash                    =3D virtnet_xdp_rx_hash,
> > > > +};
> > > > +
> > > >   static int virtnet_probe(struct virtio_device *vdev)
> > > >   {
> > > >       int i, err =3D -ENOMEM;
> > > > @@ -4613,6 +4667,8 @@ static int virtnet_probe(struct virtio_device=
 *vdev)
> > > >       dev->ethtool_ops =3D &virtnet_ethtool_ops;
> > > >       SET_NETDEV_DEV(dev, &vdev->dev);
> > > >
> > > > +     dev->xdp_metadata_ops =3D &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. */
> > >
> >