vhost: prevent features to be changed while device is running

As section 2.2 of the Virtio spec states about features
negotiation:
"During device initialization, the driver reads this and tells
the device the subset that it accepts. The only way to
renegotiate is to reset the device."

This patch implements a check to prevent illegal features change
while the device is running.

One exception is the VHOST_F_LOG_ALL feature bit, which is enabled
when live-migration is initiated. But this feature is not negotiated
with the Virtio driver, but directly with the Vhost master.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Yuanhan Liu <yliu@fridaylinux.org>

diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index fd58ad6..a3455ff 100644 (file)
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -154,7 +154,22 @@ vhost_user_set_features(struct virtio_net *dev, uint64_t features)
                return -1;
        }
 
-       if ((dev->flags & VIRTIO_DEV_RUNNING) && dev->features != features) {
+       if (dev->flags & VIRTIO_DEV_RUNNING) {
+               if (dev->features == features)
+                       return 0;
+
+               /*
+                * Error out if master tries to change features while device is
+                * in running state. The exception being VHOST_F_LOG_ALL, which
+                * is enabled when the live-migration starts.
+                */
+               if ((dev->features ^ features) & ~(1ULL << VHOST_F_LOG_ALL)) {
+                       RTE_LOG(ERR, VHOST_CONFIG,
+                               "(%d) features changed while device is running.\n",
+                               dev->vid);
+                       return -1;
+               }
+
                if (dev->notify_ops->features_changed)
                        dev->notify_ops->features_changed(dev->vid, features);
        }