Re: [PATCH net] virtio_net: sync rss_trailer.max_tx_vq on queue_pairs change via VQ_PAIRS_SET

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Apr 23, 2026 at 09:01:26AM +0200, Paolo Abeni wrote:
> On 4/16/26 11:21 PM, Brett Creeley wrote:
> > When netif_is_rxfh_configured() is true (i.e., the user has explicitly
> > configured the RSS indirection table), virtnet_set_queues() skips the
> > RSS update path and falls through to the VIRTIO_NET_CTRL_MQ_VQ_PAIRS_SET
> > command to change the number of queue pairs. However, it does not update
> > vi->rss_trailer.max_tx_vq to reflect the new queue_pairs value.
> > 
> > This causes a mismatch between vi->curr_queue_pairs and
> > vi->rss_trailer.max_tx_vq. Any subsequent RSS reconfiguration (e.g.,
> > via ethtool -X) calls virtnet_commit_rss_command(), which sends the
> > stale max_tx_vq to the device, silently reverting the queue count.
> > 
> > Reproduction:
> > 1. User configured RSS
> >   ethtool -X eth0 equal 8
> > 2. VQ_PAIRS_SET path; max_tx_vq stays 16
> >   ethtool -L eth0 combined 12
> > 3. RSS commit uses max_tx_vq=16 instead of 12
> >   ethtool -X eth0 equal 4
> > 
> > Fix this by updating vi->rss_trailer.max_tx_vq after a successful
> > VQ_PAIRS_SET command when RSS is enabled, keeping it in sync with
> > curr_queue_pairs.
> > 
> > Fixes: 50bfcaedd78e ("virtio_net: Update rss when set queue")
> > Assisted-by: Claude: claude-opus-4.6
> > Signed-off-by: Brett Creeley <brett.creeley@amd.com>
> 
> The patch LGTM, but waiting a little longer just in case the virtio crew
> has some comments.
> 
> /P

Acked-by: Michael S. Tsirkin <mst@redhat.com>