diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
index 768fb5c28c..9202b167dd 100644
--- a/docs/interop/vhost-user.rst
+++ b/docs/interop/vhost-user.rst
@@ -108,6 +108,43 @@ A vring state description
 
 :num: a 32-bit number
 
+A vring descriptor index for split virtqueues
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
++-------------+---------------------+
+| vring index | index in avail ring |
++-------------+---------------------+
+
+:vring index: 32-bit index of the respective virtqueue
+
+:index in avail ring: 32-bit value, of which currently only the lower 16
+  bits are used:
+
+  - Bits 0–15: Index of the next *Available Ring* descriptor that the
+    back-end will process.  This is a free-running index that is not
+    wrapped by the ring size.
+  - Bits 16–31: Reserved (set to zero)
+
+Vring descriptor indices for packed virtqueues
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
++-------------+--------------------+
+| vring index | descriptor indices |
++-------------+--------------------+
+
+:vring index: 32-bit index of the respective virtqueue
+
+:descriptor indices: 32-bit value:
+
+  - Bits 0–14: Index of the next *Available Ring* descriptor that the
+    back-end will process.  This is a free-running index that is not
+    wrapped by the ring size.
+  - Bit 15: Driver (Available) Ring Wrap Counter
+  - Bits 16–30: Index of the entry in the *Used Ring* where the back-end
+    will place the next descriptor.  This is a free-running index that
+    is not wrapped by the ring size.
+  - Bit 31: Device (Used) Ring Wrap Counter
+
 A vring address description
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -1042,18 +1079,50 @@ Front-end message types
 ``VHOST_USER_SET_VRING_BASE``
   :id: 10
   :equivalent ioctl: ``VHOST_SET_VRING_BASE``
-  :request payload: vring state description
+  :request payload: vring descriptor index/indices
   :reply payload: N/A
 
-  Sets the base offset in the available vring.
+  Sets the next index to use for descriptors in this vring:
+
+  * For a split virtqueue, sets only the next descriptor index to
+    process in the *Available Ring*.  The device is supposed to read the
+    next index in the *Used Ring* from the respective vring structure in
+    guest memory.
+
+  * For a packed virtqueue, both indices are supplied, as they are not
+    explicitly available in memory.
+
+  Consequently, the payload type is specific to the type of virt queue
+  (*a vring descriptor index for split virtqueues* vs. *vring descriptor
+  indices for packed virtqueues*).
 
 ``VHOST_USER_GET_VRING_BASE``
   :id: 11
   :equivalent ioctl: ``VHOST_USER_GET_VRING_BASE``
   :request payload: vring state description
-  :reply payload: vring state description
+  :reply payload: vring descriptor index/indices
 
-  Get the available vring base offset.
+  Stops the vring and returns the current descriptor index or indices:
+
+    * For a split virtqueue, returns only the 16-bit next descriptor
+      index to process in the *Available Ring*.  Note that this may
+      differ from the available ring index in the vring structure in
+      memory, which points to where the driver will put new available
+      descriptors.  For the *Used Ring*, the device only needs the next
+      descriptor index at which to put new descriptors, which is the
+      value in the vring structure in memory, so this value is not
+      covered by this message.
+
+    * For a packed virtqueue, neither index is explicitly available to
+      read from memory, so both indices (as maintained by the device) are
+      returned.
+
+  Consequently, the payload type is specific to the type of virt queue
+  (*a vring descriptor index for split virtqueues* vs. *vring descriptor
+  indices for packed virtqueues*).
+
+  The request payload’s *num* field is currently reserved and must be
+  set to 0.
 
 ``VHOST_USER_SET_VRING_KICK``
   :id: 12