OS161 TLB Miss and Page Fault

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.

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OS161 Coremap

The first concern of OS161 virtual memory system is how to manage physical pages. Generally, we can pack a physical page's information into a structure (called struct coremap_entry) and use this struct to represent a physical page. We use an array of struct coremap_entry to keep all physical pages information. This array, aka, coremap, will be one of the most important data structure in this lab.

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OS161: Arguments Passing in System Call

One principle of kernel programming is that: do not trust anything users passed in. Since we assume that users are bad, they will do anything they can to crash the kernel (just as $OS161_SRC/user/testbin/badcall/badcall.c do). So we need pay special attention to the arguments of the system calls, especially the pointers.

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