On 10/19/2023 11:54 AM, Stefano Garzarella wrote:
> On Wed, Oct 18, 2023 at 09:32:47PM +0300, Alexandru Matei wrote:
>> Once VQs are filled with empty buffers and we kick the host, it can send
>> connection requests. If 'the_virtio_vsock' is not initialized before,
>> replies are silently dropped and do not reach the host.
>
> Are replies really dropped or we just miss the notification?
>
> Could the reverse now happen, i.e., the guest wants to send a connection request, finds the pointer assigned but can't use virtqueues because they haven't been initialized yet?
>
> Perhaps to avoid your problem, we could just queue vsock->rx_work at the bottom of the probe to see if anything was queued in the meantime.
>
> Nit: please use "vsock/virtio" to point out that this problem is of the virtio transport.
>
> Thanks,
> Stefano
The replies are dropped , the scenario goes like this:
Once rx_run is set to true and rx queue is filled with empty buffers, the host sends a connection request.
The request is processed in virtio_transport_recv_pkt(), and since there is no bound socket, it calls virtio_transport_reset_no_sock() which tries to send a reset packet.
In virtio_transport_send_pkt() it checks 'the_virtio_vsock' and because it is null it exits with -ENODEV, basically dropping the packet.
I looked on your scenario and there is an issue from the moment we set the_virtio_vsock (in this patch) up until vsock->tx_run is set to TRUE.
virtio_transport_send_pkt() will queue the packet, but virtio_transport_send_pkt_work() will exit because tx_run is FALSE. This could be fixed by moving rcu_assign_pointer() after tx_run is set to TRUE.
virtio_transport_cancel_pkt() uses the rx virtqueue once the_virtio_vsock is set, so rcu_assign_pointer() should be moved after virtio_find_vqs() is called.
I think the way to go is to split virtio_vsock_vqs_init() in two: virtio_vsock_vqs_init() and virtio_vsock_vqs_fill(), as Vadim suggested. This should fix all the cases:
---
net/vmw_vsock/virtio_transport.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index ad64f403536a..1f95f98ddd3f 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -594,6 +594,11 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
vsock->tx_run = true;
mutex_unlock(&vsock->tx_lock);
+ return 0;
+}
+
+static void virtio_vsock_vqs_fill(struct virtio_vsock *vsock)
+{
mutex_lock(&vsock->rx_lock);
virtio_vsock_rx_fill(vsock);
vsock->rx_run = true;
@@ -603,8 +608,6 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
virtio_vsock_event_fill(vsock);
vsock->event_run = true;
mutex_unlock(&vsock->event_lock);
-
- return 0;
}
static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
@@ -707,6 +710,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
goto out;
rcu_assign_pointer(the_virtio_vsock, vsock);
+ virtio_vsock_vqs_fill(vsock);
mutex_unlock(&the_virtio_vsock_mutex);
@@ -779,6 +783,7 @@ static int virtio_vsock_restore(struct virtio_device *vdev)
goto out;
rcu_assign_pointer(the_virtio_vsock, vsock);
+ virtio_vsock_vqs_fill(vsock);
out:
mutex_unlock(&the_virtio_vsock_mutex);
--
