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

["Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>]

On Thu, Apr 30, 2015 at 04:11:30PM +0300, Konstantin Khlebnikov wrote:
> On Thu, Apr 30, 2015 at 2:43 PM, Konstantin Khlebnikov <koct9i-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > On Thu, Apr 30, 2015 at 12:02 AM, Linus Torvalds
> > <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> wrote:
> >> On Wed, Apr 29, 2015 at 1:44 PM, Konstantin Khlebnikov <koct9i-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 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.
> 
> Something like this (see patch in attachment)

THP is not covered.

Any comments on kcmp() idea?

-- 
 Kirill A. Shutemov