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

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在 2024/3/25 下午7:35, Xuan Zhuo 写道:
On Mon, 25 Mar 2024 04:26:08 -0700, Breno Leitao <leitao@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> 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?

Hi, Breno.

You can refer to the following modification. It is worth noting
that \field{rss_max_indirection_table_length} should only be
accessed if VIRTIO_NET_F_RSS is negotiated, which I have
modified below:

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 727c874..fb4c438 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3836,10 +3836,16 @@ static int virtnet_set_rxfh(struct net_device *dev,
        struct virtnet_info *vi = netdev_priv(dev);
        int i;

+       if (!vi->has_rss && !vi->has_rss_hash_report)
+               return -EOPNOTSUPP;
+
        if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
            rxfh->hfunc != ETH_RSS_HASH_TOP)
                return -EOPNOTSUPP;

+       if (rxfh->indir && !vi->has_rss)
+               return -EINVAL;
+
        if (rxfh->indir) {
                for (i = 0; i < vi->rss_indir_table_size; ++i)
                        vi->ctrl->rss.indirection_table[i] = rxfh->indir[i];
@@ -4757,13 +4763,14 @@ static int virtnet_probe(struct virtio_device *vdev)
        if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
                vi->has_rss_hash_report = true;

-       if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS))
+       if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS)) {
                vi->has_rss = true;
-
-       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));
+       }
+
+       if (vi->has_rss || vi->has_rss_hash_report) {
                vi->rss_key_size =
                        virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));


Regards,
Heng


@Heng Qi

Could you help us?

Thanks.


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

Thanks!





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