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Date:   Fri, 11 May 2018 08:39:52 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Prakash Sangappa <prakash.sangappa@oracle.com>
Cc:     Christopher Lameter <cl@linux.com>, linux-kernel@vger.kernel.org,
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Subject: Re: [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information
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On Thu 10-05-18 09:00:24, Prakash Sangappa wrote:
> 
> 
> On 5/10/18 12:42 AM, Michal Hocko wrote:
> > On Fri 04-05-18 09:18:11, Prakash Sangappa wrote:
> > > 
> > > On 5/4/18 4:12 AM, Michal Hocko wrote:
> > > > On Thu 03-05-18 15:39:49, prakash.sangappa wrote:
> > > > > On 05/03/2018 11:03 AM, Christopher Lameter wrote:
> > > > > > On Tue, 1 May 2018, Prakash Sangappa wrote:
> > > > > > 
> > > > > > > For analysis purpose it is useful to have numa node information
> > > > > > > corresponding mapped address ranges of the process. Currently
> > > > > > > /proc/<pid>/numa_maps provides list of numa nodes from where pages are
> > > > > > > allocated per VMA of the process. This is not useful if an user needs to
> > > > > > > determine which numa node the mapped pages are allocated from for a
> > > > > > > particular address range. It would have helped if the numa node information
> > > > > > > presented in /proc/<pid>/numa_maps was broken down by VA ranges showing the
> > > > > > > exact numa node from where the pages have been allocated.
> > > > > > Cant you write a small script that scans the information in numa_maps and
> > > > > > then displays the total pages per NUMA node and then a list of which
> > > > > > ranges have how many pages on a particular node?
> > > > > Don't think we can determine which numa node a given user process
> > > > > address range has pages from, based on the existing 'numa_maps' file.
> > > > yes we have. See move_pages...
> > > Sure using move_pages, not based on just 'numa_maps'.
> > > 
> > > > > > > reading this file will not be restricted(i.e requiring CAP_SYS_ADMIN).
> > > > > > So a prime motivator here is security restricted access to numa_maps?
> > > > > No it is the opposite. A regular user should be able to determine
> > > > > numa node information.
> > > > Well, that breaks the layout randomization, doesn't it?
> > > Exposing numa node information itself should not break randomization right?
> > I thought you planned to expose address ranges for each numa node as
> > well. /me confused.
> 
> Yes, are you suggesting this information should not be available to a
> regular
> user?

absolutely. We do check ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)
to make sure the access is authorised.
> 
> Is it not possible to get that same information using the move_pages() api
> as a regular
> user, although one / set of pages at a time?

No, see PTRACE_MODE_READ_REALCREDS check in move_pages.

-- 
Michal Hocko
SUSE Labs