In a rare event, after the vhost protocol message exchange has finished and the interface had been brought up successfully, the driver MAY still change its mind by sending new memory maps via SET_MEM_TABLE. Upon processing SET_MEM_TABLE, VPP invalidates the old memory regions and the descriptor tables. But it does not re-compute the new descriptor tables based on the new memory maps. Since VPP does not have the descriptor tables, it does not read the packets from the vring.

In the normal working case, after SET_MEM_TABLE, the driver follows up with SET_VRING_ADDRESS which VPP computes the descriptor tables.