Then all it has to do is read the tables and translate user addresses in software. However, addresses that are contiguous in the virtual address space may not be contiguous physically. Draw an example. Suppose the operating system also runs mapped. Then it must generate a page table entry for the user area.
Some machines provide special instructions to get at user stuff.
Note that under no circumstances should users be given access to mapping tables. So far we have disentangled the programmer's view of memory from the system's view using a mapping mechanism. Each sees a different organization. This makes it easier for the OS to shuffle users around and simplifies memory sharing between users. However, until now a user process had to be completely loaded into memory before it could run.