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Date: Wed, 19 Oct 2016 11:07:28 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: [PATCH 00/10] mm: adjust get_user_pages* functions to explicitly
 pass FOLL_* flags
Message-ID: <20161019090727.GE7517@dhcp22.suse.cz>
References: <20161013002020.3062-1-lstoakes@gmail.com>
 <20161018153050.GC13117@dhcp22.suse.cz>
 <20161019085815.GA22239@lucifer>
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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").

-- 
Michal Hocko
SUSE Labs