+When the VHOST_USER_PROTOCOL_F_SLAVE_REQ is supported by the slave,
and the
+master initiated the slave to master communication channel using the
+VHOST_USER_SET_SLAVE_REQ_FD request, the slave can send IOTLB miss
and access
+failure events by sending VHOST_USER_SLAVE_IOTLB_MSG requests to
the master
+with a struct vhost_iotlb_msg payload. For miss events, the iotlb
payload has
+to be filled with the miss message type (1), the I/O virtual
address and the
+permissions flags. For access failure event, the iotlb payload has
to be
+filled with the access failure message type (4), the I/O virtual
address and
+the permissions flags.
I don't think slave should cache invalid entries. If it does not,
how can it detect access failure as opposed to a miss?
Of course, invalid cache entries should not be cached.
The VHOST_IOTLB_ACCESS_FAIL has been specified for the Kernel backend,
even if the latter does not implement it yet.