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