netdev - Re: [PATCH] virtio-net: Zero max_tx_vq field for VIRTIO_NET_CTRL_MQ_HASH

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Date: Thu, 10 Aug 2023 18:41:16 +0800
From: Hawkins Jiawei <yin31149@...il.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, eperezma@...hat.com, 
	18801353760@....com, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio-net: Zero max_tx_vq field for VIRTIO_NET_CTRL_MQ_HASH_CONFIG
 case

On 2023/8/10 16:51, Michael S. Tsirkin wrote:
> On Thu, Aug 10, 2023 at 11:15:57AM +0800, Hawkins Jiawei wrote:
>> Kernel uses `struct virtio_net_ctrl_rss` to save command-specific-data
>> for both the VIRTIO_NET_CTRL_MQ_HASH_CONFIG and
>> VIRTIO_NET_CTRL_MQ_RSS_CONFIG commands.
>>
>> According to the VirtIO standard, "Field reserved MUST contain zeroes.
>> It is defined to make the structure to match the layout of
>> virtio_net_rss_config structure, defined in 5.1.6.5.7.".
>>
>> Yet for the VIRTIO_NET_CTRL_MQ_HASH_CONFIG command case, the `max_tx_vq`
>> field in struct virtio_net_ctrl_rss, which corresponds to the
>> `reserved` field in struct virtio_net_hash_config, is not zeroed,
>> thereby violating the VirtIO standard.
>>
>> This patch solves this problem by zeroing this field in
>> virtnet_init_default_rss().
>>
>> Signed-off-by: Hawkins Jiawei <yin31149@...il.com>
>
>
>
> Fixes: c7114b1249fa ("drivers/net/virtio_net: Added basic RSS support.")
> Cc: Andrew Melnychenko <andrew@...nix.com>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>
> And this is stable material I believe.

Hi Michael,

Thank you for the reminder, I will send the v2 patch with all these tags
included.

Thanks!


>
>
>
>> ---
>>
>> TestStep
>> ========
>> 1. Boot QEMU with one virtio-net-pci net device with `mq` and `hash`
>> feature on, command line like:
>>        -netdev tap,vhost=off,...
>>        -device virtio-net-pci,mq=on,hash=on,...
>>
>> 2. Trigger VIRTIO_NET_CTRL_MQ_HASH_CONFIG command in guest, command
>> line like:
>>      ethtool -K eth0 rxhash on
>>
>> Without this patch, in virtnet_commit_rss_command(), we can see the
>> `max_tx_vq` field is 1 in gdb like below:
>>
>>      pwndbg> p vi->ctrl->rss
>>      $1 = {
>>        hash_types = 63,
>>        indirection_table_mask = 0,
>>        unclassified_queue = 0,
>>        indirection_table = {0 <repeats 128 times>},
>>        max_tx_vq = 1,
>>        hash_key_length = 40 '(',
>>        ...
>>      }
>>
>> With this patch, in virtnet_commit_rss_command(), we can see the
>> `max_tx_vq` field is 0 in gdb like below:
>>
>>      pwndbg> p vi->ctrl->rss
>>      $1 = {
>>        hash_types = 63,
>>        indirection_table_mask = 0,
>>        unclassified_queue = 0,
>>        indirection_table = {0 <repeats 128 times>},
>>        max_tx_vq = 0,
>>        hash_key_length = 40 '(',
>>        ...
>>      }
>>
>>   drivers/net/virtio_net.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 1270c8d23463..8db38634ae82 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -2761,7 +2761,7 @@ static void virtnet_init_default_rss(struct virtnet_info *vi)
>>              vi->ctrl->rss.indirection_table[i] = indir_val;
>>      }
>>
>> -    vi->ctrl->rss.max_tx_vq = vi->curr_queue_pairs;
>> +    vi->ctrl->rss.max_tx_vq = vi->has_rss ? vi->curr_queue_pairs : 0;
>>      vi->ctrl->rss.hash_key_length = vi->rss_key_size;
>>
>>      netdev_rss_key_fill(vi->ctrl->rss.key, vi->rss_key_size);
>> --
>> 2.34.1
>