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

[Heng Qi <hengqi@linux.alibaba.com>]

在 2024/3/25 下午7:35, Xuan Zhuo 写道:
> 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?

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!