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

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Date: Mon, 25 Mar 2024 13:57:53 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Breno Leitao <leitao@...ian.org>
Cc: rbc@...a.com,
 riel@...riel.com,
 stable@...r.kernel.org,
 qemu-devel@...gnu.org,
 "open list:VIRTIO CORE AND NET DRIVERS" <virtualization@...ts.linux.dev>,
 "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "Michael S. Tsirkin" <mst@...hat.com>,
 Jason Wang <jasowang@...hat.com>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>,
 Andrew Melnychenko <andrew@...nix.com>
Subject: Re: [PATCH] virtio_net: Do not send RSS key if it is not supported

On Fri, 22 Mar 2024 03:21:21 -0700, Breno Leitao <leitao@...ian.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@...ian.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.

Thanks.