Sys161 will panic if you try to write a TLB entry with a entryhi, but there are already a TLB entry with the same entryhi but in a different TLB slot. This is because entryhi should be a UNIQUE key in the TLB bank.

Now we've set up user address space, it's time to handle TLB/page faults. Note that there is a difference between TLB and page faults:

• TLB fault means the hardware don't know how to translate a virtual address since the translation didn't present in any TLB entry. So the hardware raise a TLB fault to let the kernel decide how to translate that address.

• Page fault means the user program tries to access a page that is not in memory, either not yet allocated or swapped out.