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Hi ARM experts,
I have a problem in using armv8 mmu in bare-metal system:
When using the 4KB translation granule, level 1 table which use D_Block convert VA to 1GB region PA.
In Armv8 ARM page D4-1744, table lookup starts at level 0.
Is the Level 0 table a essential step to map the PA?
May I bypass the level 0 table and do mmu conversion via level 1 translation table? In other words, directly fill the L1 table address in TTBR0 register.
Thanks!!
Ash,
Thanks for your reply, it is very helpful!!
I think I misunderstood the processing of "walk" of translation tables before. I missed the T0SZ affection to translation table walk. As my understanding now, the number of T0SZ identifies the virtual address space, and the virtual address space also determines from which level the init lookup start. In case that T0SZ >= 25 (virtual address space <= 512G), like you said above, "doing this at 4KB granularity will cause translations to start at L1".
Correct
And to go even further, at 4KB granularity, setting T0SZ to be >= 34 (so that the virtual address space is <= 1 GB) will cause translations to start at L2, because a single L2 table at 4KB granularity maps 1GB (512 entries * 2MB per entry).
Got it, many thanks! Ash.