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SubjectRe: [PATCH 10/26] x86, pkeys: notify userspace about protection key faults
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On 09/25/2015 11:20 PM, Ingo Molnar wrote:
> * Dave Hansen <dave@sr71.net> wrote:
...
>> Since follow_pte() fails for all huge
>> pages, it just falls back to pulling the protection key out of the VMA,
>> which _does_ work for huge pages.
>
> That might be true for explicit hugetlb vmas, but what about transparent hugepages
> that can show up in regular vmas?

All PTEs (large or small) established under a given VMA have the same
protection key. Any change in protection key for a range will either
change or split the VMA.

So I think it's safe to rely on the VMA entirely. Well, as least as
safe as the PTE. It's definitely a wee bit racy, which I'll elaborate
on when I repost the patches.

>> I've actually removed the PTE walking and I just now use the VMA directly. I
>> don't see a ton of additional value from walking the page tables when we can get
>> what we need from the VMA.
>
> That's actually good, because it's also cheap, especially if we can get rid of the
> extra find_vma().
>
> and we (thankfully) have no non-linear vmas to worry about anymore.

Yep.


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