Re: [PATCH] i386: PAE entries must have their low word cleared first

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Hugh Dickins wrote:
On Wed, 26 Apr 2006, Keir Fraser wrote:

We cannot use pte_clear() unless we redefine it for PAE. Currently it reduces
to set_pte() which explicitly uses the wrong ordering (sets high *then* low,
because it's normally used to introduce a mapping).


I overlooked that reversal completely.  What a very good point.
I think that actually pte_clear() _does_ need to be redefined for PAE,
to reverse that ordering as you point out.  Take a look at its use in
mm/highmem.c (where a comment states it's safe against speculative
execution, but a comment can't guarantee that!): what do you think?

Speculative execution is safe I think (and so is ptep_get_and_clear_full,
because in neither case will the virtual address be visible).

Speculative prefetching + tlb instantiation, apparently no.

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