Mill Computing, Inc. Forums The Mill Architecture Security Reply To: Security

Ivan Godard
Keymaster
Post count: 627

Please distinguish alias mapping from paging. 32-bits systems don’t have enough address-space bits, so they have to reuse addresses; this is mapping,. In addition, physical pages may be present or not. For efficiency, conventional systems combine the mapping task and the paging task in one MMU/TLB machine.

With a 60-bit space the Mill has no need for mapping; there’s all the virtual space that everybody wants there for the taking. However, virtual space may still exceed physical DRAM, so there remains a need for paging, and the Mill does paging.

The paging is done in the TLB and its associated OS tables. Those are only looked at when we miss in cache and have to go to memory, and they tell where in physical memory a given virtual page is located, just as on a conventional machine. Or not located, if the page is swapped out to disk. So a Mill can still get page traps.

Mill code is position-independent (PIC), but jump table and the like have full-width pointers with virtual addresses where the code has been mapped. The underlying DRAM may be swapped out and paged back in at a different physical address, but the virtual address remains the same and the pointers still work.