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Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly pass FOLL_* flags

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On Wed 19-10-16 09:49:43, Dave Hansen wrote:
> On 10/19/2016 02:07 AM, Michal Hocko wrote:
> > On Wed 19-10-16 09:58:15, Lorenzo Stoakes wrote:
> >> On Tue, Oct 18, 2016 at 05:30:50PM +0200, Michal Hocko wrote:
> >>> I am wondering whether we can go further. E.g. it is not really clear to
> >>> me whether we need an explicit FOLL_REMOTE when we can in fact check
> >>> mm != current->mm and imply that. Maybe there are some contexts which
> >>> wouldn't work, I haven't checked.
> >>
> >> This flag is set even when /proc/self/mem is used. I've not looked deeply into
> >> this flag but perhaps accessing your own memory this way can be considered
> >> 'remote' since you're not accessing it directly. On the other hand, perhaps this
> >> is just mistaken in this case?
> > 
> > My understanding of the flag is quite limited as well. All I know it is
> > related to protection keys and it is needed to bypass protection check.
> > See arch_vma_access_permitted. See also 1b2ee1266ea6 ("mm/core: Do not
> > enforce PKEY permissions on remote mm access").
> 
> Yeah, we need the flag to tell us when PKEYs should be applied or not.
> The current task's PKRU (pkey rights register) should really only be
> used to impact access to the task's memory, but has no bearing on how a
> given task should access remote memory.

The question I had earlier was whether this has to be an explicit FOLL
flag used by g-u-p users or we can just use it internally when mm !=
current->mm

-- 
Michal Hocko
SUSE Labs

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Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Michal Hocko <mhocko@kernel.org> - 2016-10-18 17:40 +0200
  Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Michal Hocko <mhocko@kernel.org> - 2016-10-19 16:20 +0200
    Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Dave Hansen <dave.hansen@linux.intel.com> - 2016-10-19 19:00 +0200
      Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Michal Hocko <mhocko@kernel.org> - 2016-10-19 19:10 +0200
        Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Dave Hansen <dave.hansen@linux.intel.com> - 2016-10-19 19:30 +0200
          Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Michal Hocko <mhocko@kernel.org> - 2016-10-20 21:30 +0200
  Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Lorenzo Stoakes <lstoakes@gmail.com> - 2016-10-19 18:20 +0200
  Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly  pass FOLL_* flags Lorenzo Stoakes <lstoakes@gmail.com> - 2016-10-26 11:00 +0200

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