Can a TLB hit lead to page fault in memory?

memory-management operating-system kernel cpu-architecture tlb
Terminal picture Terminal · Jun 18, 2011 · Viewed 13k times · Source

In UC Berkley Video lectures on OS by John Kubiatowicz (Prof. Kuby) available on web, he mentioned that TLB hit doesn't mean that corresponding page is in main memory. Page fault can still occur.
Technically TLBs are cache for page table entry and since all page table entries don't have their corresponding page available in main memory. Same can be true for TLBs. A TLB hit may lead to page fault.

But according to algorithms given in text books I am unable to find such a case. On a TLB miss kernel refer to page tables and update the TLB cache for appropriate address translation. Next TLB hit can't lead to page fault. When kernel swap out the page, it updates the appropriate bits for that page table entry and invalidate the corresponding TLB, so there can't be a TLB hit next time until page is loaded in main memory.

So can someone stand for correctness of Prof kuby's claim and point out a case when instead of TLB hit (the translated physical address for corresponding virtual address in found in TLB), a page fault can occur?

Answer

Lyke picture Lyke · Jun 18, 2011

One example is if the memory access is different from the allowed one.

e.g. you want to write to memory that's write protected. A TLB exists, it's a hit and the address is translated. But on access you get a trap, as you're trying to write to memory that's read-only

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