Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page

[KOSAKI Motohiro]

>> +     if (!migration) {
>> +             /* re-check */
>> +             if (PageSwapCache(page) &&
>> +                 page_count(page) != page_mapcount(page) + 2) {
>> +                     /* We lose race against get_user_pages_fast() */
>> +                     set_pte_at(mm, address, pte, pteval);
>> +                     ret = SWAP_FAIL;
>> +                     goto out_unmap;
>> +             }
>> +     }
>> +     mmu_notifier_invalidate_page(vma->vm_mm, address);
>
> With regard to mmu notifier, this is the opposite of the right
> ordering. One mmu_notifier_invalidate_page must run _before_ the first
> check. The ptep_clear_flush_notify will then stay and there's no need
> of a further mmu_notifier_invalidate_page after the second check.

OK. but I have one question.

Can we assume mmu_notifier is only used by kvm now?
if not, we need to make new notifier.
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