Re: [Qemu-devel] [PATCH] net/virtio: fix multi-queue negotiation

[Marcel Apfelbaum <marcel.apfelbaum@gmail.com>]

On 06/23/2015 01:56 PM, Michael S. Tsirkin wrote:
> On Tue, Jun 23, 2015 at 01:23:10PM +0300, Marcel Apfelbaum wrote:
>> On 06/23/2015 12:57 PM, Michael S. Tsirkin wrote:
>>> On Thu, Jun 18, 2015 at 09:05:44PM +0300, Marcel Apfelbaum wrote:
>>>> Clear host multi-queue related features if the peer
>>>> doesn't support it.
>>>>
>>>> Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
>>>> ---
>>>> Notes:
>>>>   This fixes a guest CPU soft lock, however the virtio-net
>>>>   device will not work correctly. It seems that is
>>>>   peer's "fault", not knowing how to handle the situation.
>>>>   However, I submit this patch since it corrects the negotiation
>>>>   and saves us from a guest crash (!).
>>>>
>>>>   Any ideas from the virtio/multi-queue developers on how to debug
>>>>   this further are welcomed.
>>>>
>>>>   hw/net/virtio-net.c | 13 ++++++++++++-
>>>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>>> index 9281aa1..63e59e8 100644
>>>> --- a/hw/net/virtio-net.c
>>>> +++ b/hw/net/virtio-net.c
>>>> @@ -367,6 +367,11 @@ static int peer_has_ufo(VirtIONet *n)
>>>>       return n->has_ufo;
>>>>   }
>>>>
>>>> +static int peer_has_multiqueue(VirtIONet *n)
>>>> +{
>>>> +    return n->multiqueue;
>>>> +}
>>>> +
>>>>   static void virtio_net_set_mrg_rx_bufs(VirtIONet *n, int mergeable_rx_bufs,
>>>>                                          int version_1)
>>>>   {
>>>> @@ -469,6 +474,13 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features)
>>>>           virtio_clear_feature(&features, VIRTIO_NET_F_HOST_UFO);
>>>>       }
>>>>
>>>> +    if (!peer_has_multiqueue(n)) {
>>>> +        virtio_clear_feature(&features, VIRTIO_NET_F_MQ);
>>>> +        virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ANNOUNCE);
>>>> +        virtio_clear_feature(&features, VIRTIO_NET_F_CTRL_VQ);
>>>> +        virtio_clear_feature(&features, VIRTIO_NET_F_CTRL_RX);
>>>> +    }
>>>> +
>>>>       if (!get_vhost_net(nc->peer)) {
>>>>           virtio_add_feature(&features, VIRTIO_F_VERSION_1);
>>>>           return features;
>>>
>>> _MQ makes sense but what about the rest? Why clear them?
>> Guest's virtio driver doesn't like if MQ is off and any of the other flags remains ON.
>> It has a specific check for each of them and fails the loading if not all are off.
>>
>> Thanks,
>> Marcel
>
>
> I think you are mistaken.
>
>          if (!virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) &&
>              (VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_RX,
>                               "VIRTIO_NET_F_CTRL_VQ") ||
>               VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_VLAN,
>                               "VIRTIO_NET_F_CTRL_VQ") ||
>               VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_GUEST_ANNOUNCE,
>                               "VIRTIO_NET_F_CTRL_VQ") ||
>               VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_MQ, "VIRTIO_NET_F_CTRL_VQ") ||
>               VIRTNET_FAIL_ON(vdev, VIRTIO_NET_F_CTRL_MAC_ADDR,
>                               "VIRTIO_NET_F_CTRL_VQ"))) {
>                  return false;
>          }
>
>          return true;
>
> So if CTRL VQ is not set, you can not have MQ or any of the others.
>
Hmm, I know what saw, but I don't fully understand why is happening.
I'll give another try and I'll return with more info.

Thanks,
Marcel

>
>
>>>
>>>> @@ -1314,7 +1326,6 @@ static void virtio_net_tx_bh(void *opaque)
>>>>   static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
>>>>   {
>>>>       n->multiqueue = multiqueue;
>>>> -
>>>>       virtio_net_set_queues(n);
>>>>   }
>>>>
>>>> --
>>>> 2.1.0
>