Re: [PATCH] virtio_net: Do not send RSS key if it is not supported

[Xuan Zhuo]

On Mon, 25 Mar 2024 04:26:08 -0700, Breno Leitao <leitao@debian.org> wrote:
> Hello Xuan,
>
> On Mon, Mar 25, 2024 at 01:57:53PM +0800, Xuan Zhuo wrote:
> > On Fri, 22 Mar 2024 03:21:21 -0700, Breno Leitao <leitao@debian.org> wrote:
> > > Hello Xuan,
> > >
> > > On Fri, Mar 22, 2024 at 10:00:22AM +0800, Xuan Zhuo wrote:
> > > > On Thu, 21 Mar 2024 09:54:30 -0700, Breno Leitao <leitao@debian.org> 
> > > > wrote:
> > >
> > > > > 4) Since the command above does not have a key, then the last
> > > > >    scatter-gatter entry will be zeroed, since rss_key_size == 0.
> > > > >     sg_buf_size = vi->rss_key_size;
> > > >
> > > >
> > > >
> > > >         if (vi->has_rss || vi->has_rss_hash_report) {
> > > >                 vi->rss_indir_table_size =
> > > >                         virtio_cread16(vdev, offsetof(struct 
> > > > virtio_net_config,
> > > >                                 rss_max_indirection_table_length));
> > > >                 vi->rss_key_size =
> > > >                         virtio_cread8(vdev, offsetof(struct 
> > > > virtio_net_config, rss_max_key_size));
> > > >
> > > >                 vi->rss_hash_types_supported =
> > > >                     virtio_cread32(vdev, offsetof(struct 
> > > > virtio_net_config, supported_hash_types));
> > > >                 vi->rss_hash_types_supported &=
> > > >                                 ~(VIRTIO_NET_RSS_HASH_TYPE_IP_EX |
> > > >                                   VIRTIO_NET_RSS_HASH_TYPE_TCP_EX |
> > > >                                   VIRTIO_NET_RSS_HASH_TYPE_UDP_EX);
> > > >
> > > >                 dev->hw_features |= NETIF_F_RXHASH;
> > > >         }
> > > >
> > > >
> > > > vi->rss_key_size is initiated here, I wonder if there is something 
> > > > wrong?
> > >
> > > Not really, the code above is never executed (in my machines). This is
> > > because `vi->has_rss` and `vi->has_rss_hash_report` are both unset.
> > >
> > > Looking further, vdev does not have the VIRTIO_NET_F_RSS and
> > > VIRTIO_NET_F_HASH_REPORT features.
> > >
> > > Also, when I run `ethtool -x`, I got:
> > >
> > >   # ethtool  -x eth0
> > >   RX flow hash indirection table for eth0 with 1 RX ring(s):
> > >   Operation not supported
> > >   RSS hash key:
> > >   Operation not supported
> > >   RSS hash function:
> > >       toeplitz: on
> > >       xor: off
> > >       crc32: off
> >
> >
> > The spec saies:
> >     Note that if the device offers VIRTIO_NET_F_HASH_REPORT, even if it
> >     supports only one pair of virtqueues, it MUST support at least one of
> >     commands of VIRTIO_NET_CTRL_MQ class to configure reported hash
> >     parameters:
> >
> >     If the device offers VIRTIO_NET_F_RSS, it MUST support
> >     VIRTIO_NET_CTRL_MQ_RSS_CONFIG command per 5.1.6.5.7.1.
> >
> >     Otherwise the device MUST support VIRTIO_NET_CTRL_MQ_HASH_CONFIG command
> >     per 5.1.6.5.6.4.
> >
> >
> > So if we have not anyone of `vi->has_rss` and `vi->has_rss_hash_report`,
> > we should return from virtnet_set_rxfh directly.
>
> Makes sense. Although it is not clear to me how vi->has_rss_hash_report
> is related here, but, I am convinced that we shouldn't do any RSS
> operation if the device doesn't have the RSS feature, i.e, vi->has_rss
> is false.
>
> That said, I am thinking about something like this. How does it sound?
>
>       diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>       index 5a7700b103f8..8c1ad7361cf2 100644
>       --- a/drivers/net/virtio_net.c
>       +++ b/drivers/net/virtio_net.c
>       @@ -3780,6 +3780,9 @@ static int virtnet_set_rxfh(struct net_device 
> *dev,
>               struct virtnet_info *vi = netdev_priv(dev);
>               int i;
>
>       +       if (!vi->has_rss)
>       +               return -EOPNOTSUPP;
>       +

Should we check has_rss_hash_report?

@Heng Qi

Could you help us?

Thanks.


>               if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
>                   rxfh->hfunc != ETH_RSS_HASH_TOP)
>                       return -EOPNOTSUPP;
>
> Thanks!