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, 5 insertions, 1 deletions

diff --git a/src/vnet/devices/virtio/vhost_user.api b/src/vnet/devices/virtio/vhost_user.api
index 9b057552c00..127b0a27fc7 100644
--- a/src/vnet/devices/virtio/vhost_user.api
+++ b/src/vnet/devices/virtio/vhost_user.api
@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-option version = "4.0.0";
+option version = "4.0.1";
 
 import "vnet/interface_types.api";
 import "vnet/ethernet/ethernet_types.api";
@@ -27,6 +27,7 @@ import "vnet/devices/virtio/virtio_types.api";
     @param disable_mrg_rxbuf - disable the use of merge receive buffers
     @param disable_indirect_desc - disable the use of indirect descriptors which driver can use
     @param enable_gso - enable gso support (default 0)
+    @param enable_packed - enable packed ring support (default 0)
     @param mac_address - hardware address to use if 'use_custom_mac' is set
 */
 define create_vhost_user_if
@@ -39,6 +40,7 @@ define create_vhost_user_if
   bool disable_mrg_rxbuf;
   bool disable_indirect_desc;
   bool enable_gso;
+  bool enable_packed;
   u32 custom_dev_instance;
   bool use_custom_mac;
   vl_api_mac_address_t mac_address;
@@ -62,6 +64,7 @@ define create_vhost_user_if_reply
     @param is_server - our side is socket server
     @param sock_filename - unix socket filename, used to speak with frontend
     @param enable_gso - enable gso support (default 0)
+    @param enable_packed - enable packed ring support (default 0)
 */
 autoreply define modify_vhost_user_if
 {
@@ -72,6 +75,7 @@ autoreply define modify_vhost_user_if
   string sock_filename[256];
   bool renumber;
   bool enable_gso;
+  bool enable_packed;
   u32 custom_dev_instance;
 };