极术小姐姐 · 2020年02月03日

Is it necessary to flush data cache 3

A-R-M seems not mention anything about this data cache flush of changing table entry.
From A-R-M of ARMv8-Cortex-A (DDI 0487D.a), the G.5.9 TLB maintenance requirements,
we do not see any hint about the necessary to flush data cache of table entry.

The only one example for a uniprocessor system in G.5.9.1, there is no data cache flush operation.

Therefore, in a uniprocessor system, an example instruction sequence for writing a translation table entry, covering
changes to the instruction or data mappings is:

STR rx, [Translation table entry] ; write new entry to the translation table
DSB ; ensures visibility of the new entry
Invalidate TLB entry by VA (and ASID if non-global) [page address]
Invalidate BTC
DSB ; ensure completion of the Invalidate TLB instruction
ISB ; ensure table changes visible to instruction fetch

For SMP system, It neither not find anything about necessary of data cache flush operation.

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棋子 · 2020年02月03日

After I correct the MMU.IRGN setting, it works without flushing data cache of modified page entry.

Thus, Q1 is also solved. Because MMU page walk is not non-cached, for wrong setting as "write-through".

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