netdev - Re: [PATCH net-next] virtio_net: implement VIRTIO_CONFIG_S_NEEDS

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Date:   Tue, 17 Oct 2017 11:05:07 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] virtio_net: implement
 VIRTIO_CONFIG_S_NEEDS_RESET



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 <mst@...hat.com> 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 <mst@...hat.com> 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