virtio: support virtio 1.1 packed ring in vhost

virtio 1.1 defines a number of new features. Packed ring is among the most
notable and important one. It combines used, available, and descripptor rings
into one.

This patch provides experimental support for packed ring. To avoid
regression, when packed ring is configured for the interface, it is branched
to a separate RX and TX driver. Non packed ring should continue to perform
as it was before.

Packed ring is tested using qemu4.2 and ubuntu focal fossa (kernel 5.4.0-12)
on the guess VM which supports packed ring.

To configure VPP with packed ring, just add the optional keyword "packed"
when creating the vhost interface. To bring up the guest VM with packed ring,
add "packed=on" in the qemu launch command.

To facilitate troubleshooting, also added "verbose" option in
show vhost desc CLI to include displaying the indirect descriptors.

Known qemu reconnect issue -
If VPP is restarted, guest VMs also need to be restarted. The problem
is kernel virtio-net-pci keeps track of the previous available and used
indices. For virtio 1.0, these indices are in shared memory and qemu can
easily copy them to pass to the backend for reconnect. For virio 1.1, these
indices are no longer in shared memory. Qemu needs a new mechanism to retrieve
them and it is not currently implemented. So when the protocol reconnects,
qemu does not have the correct available and used indices to pass to the
backend. As a result, after the reconnect, virtio-net-pci is reading the TX
ring from the wrong position in the ring, not the same position which the
backend is writing. Similar problem exists also in the RX.

Type: feature

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: I5afc50b0bafab5a1de7a6dd10f399db3fafd144c

1 files changed, 12 insertions, 8 deletions

diff --git a/src/vnet/devices/virtio/vhost_user_api.c b/src/vnet/devices/virtio/vhost_user_api.c
index 2ab87a65690..67365334d95 100644
--- a/src/vnet/devices/virtio/vhost_user_api.c
+++ b/src/vnet/devices/virtio/vhost_user_api.c
@@ -71,10 +71,12 @@ vl_api_create_vhost_user_if_t_handler (vl_api_create_vhost_user_if_t * mp)
     disabled_features |= (1ULL << FEAT_VIRTIO_F_INDIRECT_DESC);
 
   /*
-   * feature mask is not supported via binary API. We disable GSO feature in the
-   * feature mask. It may be enabled via enable_gso argument.
+   * GSO and PACKED are not supported by feature mask via binary API. We
+   * disable GSO and PACKED feature in the feature mask. They may be enabled
+   * explicitly via enable_gso and enable_packed argument
    */
-  disabled_features |= FEATURE_VIRTIO_NET_F_HOST_GUEST_TSO_FEATURE_BITS;
+  disabled_features |= FEATURE_VIRTIO_NET_F_HOST_GUEST_TSO_FEATURE_BITS |
+    (1ULL << FEAT_VIRTIO_F_RING_PACKED);
   features &= ~disabled_features;
 
   if (mp->use_custom_mac)
@@ -86,7 +88,7 @@ vl_api_create_vhost_user_if_t_handler (vl_api_create_vhost_user_if_t * mp)
   rv = vhost_user_create_if (vnm, vm, (char *) mp->sock_filename,
 			     mp->is_server, &sw_if_index, features,
 			     mp->renumber, ntohl (mp->custom_dev_instance),
-			     mac_p, mp->enable_gso);
+			     mac_p, mp->enable_gso, mp->enable_packed);
 
   /* Remember an interface tag for the new interface */
   if (rv == 0)
@@ -122,16 +124,18 @@ vl_api_modify_vhost_user_if_t_handler (vl_api_modify_vhost_user_if_t * mp)
   vlib_main_t *vm = vlib_get_main ();
 
   /*
-   * feature mask is not supported via binary API. We disable GSO feature in the
-   * feature mask. It may be enabled via enable_gso argument.
+   * GSO and PACKED are not supported by feature mask via binary API. We
+   * disable GSO and PACKED feature in the feature mask. They may be enabled
+   * explicitly via enable_gso and enable_packed argument
    */
-  disabled_features |= FEATURE_VIRTIO_NET_F_HOST_GUEST_TSO_FEATURE_BITS;
+  disabled_features |= FEATURE_VIRTIO_NET_F_HOST_GUEST_TSO_FEATURE_BITS |
+    (1ULL << FEAT_VIRTIO_F_RING_PACKED);
   features &= ~disabled_features;
 
   rv = vhost_user_modify_if (vnm, vm, (char *) mp->sock_filename,
 			     mp->is_server, sw_if_index, features,
 			     mp->renumber, ntohl (mp->custom_dev_instance),
-			     mp->enable_gso);
+			     mp->enable_gso, mp->enable_packed);
 
   REPLY_MACRO (VL_API_MODIFY_VHOST_USER_IF_REPLY);
 }