Notes:
This is the standard blocks picture which has probably appeared in every UML slide slow. It shows the host kernel, consisting of a hardware-dependent layer talking to the hardware and a hardware-independent layer which talks to the interface exposed by the hardware layer.
Above that is the system call interface exposed by the generic kernel which is used by Linux processes.
Analogous to this is the UML picture above that. It consists of the same layers, except that its "hardware" layer talks to the host system call interface. Everything above that is the same, and if UML and the host Linux are the same kernel version, then the generic kernel piece is exactly the same code.