* mprotect: No. The difference is at most one additional locked
instruction for each pte.
* munmap(anon): No. We must handle delayed accessed anyway (don't call
free_pages_ok() until flush_tlb_ipi returned). The difference is that we
might have to perform a second pass to clear any spurious 0x40 bits.
* munmap(file): No. Second pass required for correct msync behaviour.
* try_to_swap_out(): No. another memory read.
Any other cases?
>
> Ben, fancy writing a boot-time test?
>
I'd never rely on such a test - what if the cpu checks in 99% of the
cases, but doesn't handle some cases ('rep movd, everything unaligned,
...'. And check the Pentium III erratas. There is one with the tlb
that's only triggered if 4 instruction lie in a certain window and all
access memory in the same way of the tlb (EFLAGS incorrect if 'andl
mask,<memory_addr>' causes page fault)).
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