[ovs-dev] [PATCH v2] netdev-dpdk: Avoid reconfiguration on reconnection of same vhost device.

[Ilya Maximets]

Binding/unbinding of virtio driver inside VM leads to reconfiguration
of PMD threads. This behaviour may be abused by executing bind/unbind
in an infinite loop to break normal networking on all ports attached
to the same instance of Open vSwitch.

Fix that by avoiding reconfiguration if it's not necessary.
Number of queues will not be decreased to 1 on device disconnection but
it's not very important in comparison with possible DOS attack from the
inside of guest OS.

Fixes: 81acebdaaf27 ("netdev-dpdk: Obtain number of queues for vhost
                      ports from attached virtio.")
Reported-by: Ciara Loftus <ciara.loftus at intel.com>
Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
---

Version 2:
	* Set 'vhost_reconfigured' flag if reconfiguration not
	  required.
	* Rebased on current master.

 lib/netdev-dpdk.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index b671601..ea0e16e 100644
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -2299,10 +2299,17 @@ new_device(int vid)
                 newnode = dev->socket_id;
             }
 
-            dev->requested_socket_id = newnode;
-            dev->requested_n_rxq = qp_num;
-            dev->requested_n_txq = qp_num;
-            netdev_request_reconfigure(&dev->up);
+            if (dev->requested_n_txq != qp_num
+                || dev->requested_n_rxq != qp_num
+                || dev->requested_socket_id != newnode) {
+                dev->requested_socket_id = newnode;
+                dev->requested_n_rxq = qp_num;
+                dev->requested_n_txq = qp_num;
+                netdev_request_reconfigure(&dev->up);
+            } else {
+                /* Reconfiguration not required. */
+                dev->vhost_reconfigured = true;
+            }
 
             ovsrcu_index_set(&dev->vid, vid);
             exists = true;
@@ -2362,11 +2369,7 @@ destroy_device(int vid)
             ovs_mutex_lock(&dev->mutex);
             dev->vhost_reconfigured = false;
             ovsrcu_index_set(&dev->vid, -1);
-            /* Clear tx/rx queue settings. */
             netdev_dpdk_txq_map_clear(dev);
-            dev->requested_n_rxq = NR_QUEUE;
-            dev->requested_n_txq = NR_QUEUE;
-            netdev_request_reconfigure(&dev->up);
 
             netdev_change_seq_changed(&dev->up);
             ovs_mutex_unlock(&dev->mutex);
-- 
2.7.4