Re: Regression: Requiring CAP_SYS_ADMIN for /proc/<pid>/pagemap causes application-level breakage

[Konstantin Khlebnikov]

On Thu, Apr 30, 2015 at 12:02 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Apr 29, 2015 at 1:44 PM, Konstantin Khlebnikov <koct9i@xxxxxxxxx> wrote:
>>
>> This's no longer true. After recent fixes for "anon_vma endless growing" new vma
>> might reuse old anon_vma from grandparent vma.
>
> Oh well. I guess that was too simple.
>
> If Mark is ok with the rule that "it's not reliably if you have two
> nested forks" (ie it only works if you exec for every fork you do), it
> should still work, right? It sounds like Mark doesn't necessarily need
> to handle the *generic* case.

What about exposing shared/exclusive bit in pagemap == 1 if
page_mapcount() > 1, otherwise 0 (or vise versa).

Seems like this should work for detecting CoWed pages in child mm.
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