Subject: Re: [PATCH net-next] virtio_net: implement VIRTIO_CONFIG_S_NEEDS_RESET

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 17 Oct 2017 06:44:06 +0300

On Tue, Oct 17, 2017 at 11:05:07AM +0800, Jason Wang wrote:
> 
> 
> On 2017年10月17日 06:34, Willem de Bruijn wrote:
> > On Mon, Oct 16, 2017 at 12:38 PM, Michael S. Tsirkin <[email-masked]> wrote:
> > > On Mon, Oct 16, 2017 at 12:04:57PM -0400, Willem de Bruijn wrote:
> > > > On Mon, Oct 16, 2017 at 11:31 AM, Michael S. Tsirkin <[email-masked]> wrote:
> > > > > On Mon, Oct 16, 2017 at 11:03:18AM -0400, Willem de Bruijn wrote:
> > > > > > > > +static int virtnet_reset(struct virtnet_info *vi)
> > > > > > > > +{
> > > > > > > > +     struct virtio_device *dev = vi->vdev;
> > > > > > > > +     int ret;
> > > > > > > > +
> > > > > > > > +     virtio_config_disable(dev);
> > > > > > > > +     dev->failed = dev->config->get_status(dev) & VIRTIO_CONFIG_S_FAILED;
> > > > > > > > +     virtnet_freeze_down(dev, true);
> > > > > > > > +     remove_vq_common(vi);
> > > > > > > > +
> > > > > > > > +     virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
> > > > > > > > +     virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER);
> > > > > > > > +
> > > > > > > > +     ret = virtio_finalize_features(dev);
> > > > > > > > +     if (ret)
> > > > > > > > +             goto err;
> > > > > > > > +
> > > > > > > > +     ret = virtnet_restore_up(dev);
> > > > > > > > +     if (ret)
> > > > > > > > +             goto err;
> > > > > > > > +
> > > > > > > > +     ret = virtnet_set_queues(vi, vi->curr_queue_pairs);
> > > > > > > > +     if (ret)
> > > > > > > > +             goto err;
> > > > > > > > +
> > > > > > > > +     virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> > > > > > > > +     virtio_config_enable(dev);
> > > > > > > > +     return 0;
> > > > > > > > +
> > > > > > > > +err:
> > > > > > > > +     virtio_add_status(dev, VIRTIO_CONFIG_S_FAILED);
> > > > > > > > +     return ret;
> > > > > > > > +}
> > > > > > > > +
> > > > > > > >   static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
> > > > > > > >   {
> > > > > > > >        struct scatterlist sg;
> > > > > > > I have a question here though. How do things like MAC address
> > > > > > > get restored?
> > > > > > > 
> > > > > > > What about the rx mode?
> > > > > > > 
> > > > > > > vlans?
> > > > > > The function as is releases and reinitializes only ring state.
> > > > > > Device configuration such as mac and vlan persist across
> > > > > > the reset.
> > > > > What gave you this impression? Take a look at e.g. this
> > > > > code in qemu:
> > > > > 
> > > > > static void virtio_net_reset(VirtIODevice *vdev)
> > > > > {
> > > > >      VirtIONet *n = VIRTIO_NET(vdev);
> > > > > 
> > > > >      /* Reset back to compatibility mode */
> > > > >      n->promisc = 1;
> > > > >      n->allmulti = 0;
> > > > >      n->alluni = 0;
> > > > >      n->nomulti = 0;
> > > > >      n->nouni = 0;
> > > > >      n->nobcast = 0;
> > > > >      /* multiqueue is disabled by default */
> > > > >      n->curr_queues = 1;
> > > > >      timer_del(n->announce_timer);
> > > > >      n->announce_counter = 0;
> > > > >      n->status &= ~VIRTIO_NET_S_ANNOUNCE;
> > > > > 
> > > > >      /* Flush any MAC and VLAN filter table state */
> > > > >      n->mac_table.in_use = 0;
> > > > >      n->mac_table.first_multi = 0;
> > > > >      n->mac_table.multi_overflow = 0;
> > > > >      n->mac_table.uni_overflow = 0;
> > > > >      memset(n->mac_table.macs, 0, MAC_TABLE_ENTRIES * ETH_ALEN);
> > > > >      memcpy(&n->mac[0], &n->nic->conf->macaddr, sizeof(n->mac));
> > > > >      qemu_format_nic_info_str(qemu_get_queue(n->nic), n->mac);
> > > > >      memset(n->vlans, 0, MAX_VLAN >> 3);
> > > > > }
> > > > > 
> > > > > So device seems to lose all state, you have to re-program it.
> > > > Oh, indeed! The guest does not reset its state, so it might
> > > > be out of sync with the host after the operation. Was this not
> > > > an issue when previously resetting in the context of xdp?
> > > I suspect it was broken back then, too.
> > Okay. I guess that in principle this is all programmable through
> > virtnet_set_rx_mode, virtnet_vlan_rx_add_vid, etc. But it's a
> > lot more complex than just restoring virtnet_reset. Will need to
> > be careful about concurrency issues at the least. Similar to the
> > ones you point out below.
> > 
> 
> The problem has been pointed out during developing virtio-net XDP. But it
> may not be a big issue since vhost_net ignores all kinds of the filters now.
> 
> Thanks

It might not keep doing that in the future though.
And virtio-net in userspace doesn't ignore the filters.

-- 
MST