Re: [PATCH net v3] virtio_net: Do not send RSS key if it is not supported

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

在 2024/4/1 上午4:20, Michael S. Tsirkin 写道:
> On Fri, Mar 29, 2024 at 10:16:41AM -0700, Breno Leitao wrote:
>> There is a bug when setting the RSS options in virtio_net that can break
>> the whole machine, getting the kernel into an infinite loop.
>>
>> Running the following command in any QEMU virtual machine with virtionet
>> will reproduce this problem:
>>
>>      # ethtool -X eth0  hfunc toeplitz
>>
>> This is how the problem happens:
>>
>> 1) ethtool_set_rxfh() calls virtnet_set_rxfh()
>>
>> 2) virtnet_set_rxfh() calls virtnet_commit_rss_command()
>>
>> 3) virtnet_commit_rss_command() populates 4 entries for the rss
>> scatter-gather
>>
>> 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;
>>
>> 5) This buffer is passed to qemu, but qemu is not happy with a buffer
>> with zero length, and do the following in virtqueue_map_desc() (QEMU
>> function):
>>
>>    if (!sz) {
>>        virtio_error(vdev, "virtio: zero sized buffers are not allowed");
>>
>> 6) virtio_error() (also QEMU function) set the device as broken
>>
>>      vdev->broken = true;
>>
>> 7) Qemu bails out, and do not repond this crazy kernel.
>>
>> 8) The kernel is waiting for the response to come back (function
>> virtnet_send_command())
>>
>> 9) The kernel is waiting doing the following :
>>
>>        while (!virtqueue_get_buf(vi->cvq, &tmp) &&
>> 	     !virtqueue_is_broken(vi->cvq))
>> 	      cpu_relax();
>>
>> 10) None of the following functions above is true, thus, the kernel
>> loops here forever. Keeping in mind that virtqueue_is_broken() does
>> not look at the qemu `vdev->broken`, so, it never realizes that the
>> vitio is broken at QEMU side.
>>
>> Fix it by not sending RSS commands if the feature is not available in
>> the device.
>>
>> Fixes: c7114b1249fa ("drivers/net/virtio_net: Added basic RSS support.")
>> Cc: stable@vger.kernel.org
> net has its own stable process, don't CC stable on net patches.
>
>
>> Cc: qemu-devel@nongnu.org
>> Signed-off-by: Breno Leitao <leitao@debian.org>
>> ---
>> Changelog:
>>
>> V2:
>>    * Moved from creating a valid packet, by rejecting the request
>>      completely
>> V3:
>>    * Got some good feedback from and Xuan Zhuo and Heng Qi, and reworked
>>      the rejection path.
>>
>> ---
>>   drivers/net/virtio_net.c | 22 ++++++++++++++++++----
>>   1 file changed, 18 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index c22d1118a133..c4a21ec51adf 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -3807,6 +3807,7 @@ static int virtnet_set_rxfh(struct net_device *dev,
>>   			    struct netlink_ext_ack *extack)
>>   {
>>   	struct virtnet_info *vi = netdev_priv(dev);
>> +	bool update = false;
>>   	int i;
>>   
>>   	if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
>> @@ -3814,13 +3815,24 @@ static int virtnet_set_rxfh(struct net_device *dev,
>>   		return -EOPNOTSUPP;
>>   
>>   	if (rxfh->indir) {
>> +		if (!vi->has_rss)
>> +			return -EOPNOTSUPP;
>> +
>>   		for (i = 0; i < vi->rss_indir_table_size; ++i)
>>   			vi->ctrl->rss.indirection_table[i] = rxfh->indir[i];
>> +		update = true;
>>   	}
>> -	if (rxfh->key)
>> +
>> +	if (rxfh->key) {
>> +		if (!vi->has_rss && !vi->has_rss_hash_report)
>> +			return -EOPNOTSUPP;
>
> What's the logic here? Is it || or &&? A comment can't hurt.

&&

Hi Breno,

You can add a comment like the following:

If either _F_HASH_REPORT or _F_RSS are negotiated, the device provides
hash calculation capabilities, that is, hash_key can be configured.

Regards,
Heng

>
>> +
>>   		memcpy(vi->ctrl->rss.key, rxfh->key, vi->rss_key_size);
>> +		update = true;
>> +	}
>>   
>> -	virtnet_commit_rss_command(vi);
>> +	if (update)
>> +		virtnet_commit_rss_command(vi);
>>   
>>   	return 0;
>>   }
>> @@ -4729,13 +4741,15 @@ 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));
>>   
>> -- 
>> 2.43.0