From: Jann Horn <jannh@google.com>
To: Prakash Sangappa <prakash.sangappa@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Dave Hansen <dave.hansen@intel.com>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
kernel list <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
Linux API <linux-api@vger.kernel.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
n-horiguchi@ah.jp.nec.com, Ulrich Drepper <drepper@gmail.com>,
David Rientjes <rientjes@google.com>,
Horiguchi Naoya <nao.horiguchi@gmail.com>,
steven.sistare@oracle.com
Subject: Re: [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information
Date: Fri, 14 Sep 2018 20:14:04 +0200 [thread overview]
Message-ID: <CAG48ez2tDrz9VBx-9mpwVTqckPj-YTw6foF-Ecr8FKWXL9Zing@mail.gmail.com> (raw)
In-Reply-To: <a1834be4-0f8e-9d07-1013-7477d3a5e6be@oracle.com>
On Fri, Sep 14, 2018 at 8:08 PM Prakash Sangappa
<prakash.sangappa@oracle.com> wrote:
> On 9/14/18 5:49 AM, Jann Horn wrote:
> > On Fri, Sep 14, 2018 at 8:21 AM Michal Hocko <mhocko@kernel.org> wrote:
> >> On Fri 14-09-18 03:33:28, Jann Horn wrote:
> >>> On Wed, Sep 12, 2018 at 10:43 PM prakash.sangappa
> >>> <prakash.sangappa@oracle.com> wrote:
> >>>> On 05/09/2018 04:31 PM, Dave Hansen wrote:
> >>>>> On 05/07/2018 06:16 PM, prakash.sangappa wrote:
> >>>>>> It will be /proc/<pid>/numa_vamaps. Yes, the behavior will be
> >>>>>> different with respect to seeking. Output will still be text and
> >>>>>> the format will be same.
> >>>>>>
> >>>>>> I want to get feedback on this approach.
> >>>>> I think it would be really great if you can write down a list of the
> >>>>> things you actually want to accomplish. Dare I say: you need a
> >>>>> requirements list.
> >>>>>
> >>>>> The numa_vamaps approach continues down the path of an ever-growing list
> >>>>> of highly-specialized /proc/<pid> files. I don't think that is
> >>>>> sustainable, even if it has been our trajectory for many years.
> >>>>>
> >>>>> Pagemap wasn't exactly a shining example of us getting new ABIs right,
> >>>>> but it sounds like something along those is what we need.
> >>>> Just sent out a V2 patch. This patch simplifies the file content. It
> >>>> only provides VA range to numa node id information.
> >>>>
> >>>> The requirement is basically observability for performance analysis.
> >>>>
> >>>> - Need to be able to determine VA range to numa node id information.
> >>>> Which also gives an idea of which range has memory allocated.
> >>>>
> >>>> - The proc file /proc/<pid>/numa_vamaps is in text so it is easy to
> >>>> directly view.
> >>>>
> >>>> The V2 patch supports seeking to a particular process VA from where
> >>>> the application could read the VA to numa node id information.
> >>>>
> >>>> Also added the 'PTRACE_MODE_READ_REALCREDS' check when opening the
> >>>> file /proc file as was indicated by Michal Hacko
> >>> procfs files should use PTRACE_MODE_*_FSCREDS, not PTRACE_MODE_*_REALCREDS.
> >> Out of my curiosity, what is the semantic difference? At least
> >> kernel_move_pages uses PTRACE_MODE_READ_REALCREDS. Is this a bug?
> > No, that's fine. REALCREDS basically means "look at the caller's real
> > UID for the access check", while FSCREDS means "look at the caller's
> > filesystem UID". The ptrace access check has historically been using
> > the real UID, which is sorta weird, but normally works fine. Given
> > that this is documented, I didn't see any reason to change it for most
> > things that do ptrace access checks, even if the EUID would IMO be
> > more appropriate. But things that capture caller credentials at points
> > like open() really shouldn't look at the real UID; instead, they
> > should use the filesystem UID (which in practice is basically the same
> > as the EUID).
> >
> > So in short, it depends on the interface you're coming through: Direct
> > syscalls use REALCREDS, things that go through the VFS layer use
> > FSCREDS.
>
> So in this case can the REALCREDS check be done in the read() system call
> when reading the /proc file instead of the open call?
No, REALCREDS shouldn't be used in open() and shouldn't be used in read().
FSCREDS can be used in open(); in theory, using ptrace_may_access() in
any way in read() is currently unsafe, but in practice, it's used that
way anyway. I have plans to clean that up eventually...
next prev parent reply other threads:[~2018-09-14 18:14 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-02 5:58 [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information Prakash Sangappa
2018-05-02 21:33 ` Andrew Morton
2018-05-02 22:28 ` Dave Hansen
2018-05-02 23:17 ` prakash.sangappa
2018-05-03 8:46 ` Anshuman Khandual
2018-05-03 22:27 ` prakash.sangappa
2018-05-03 22:26 ` Dave Hansen
2018-05-07 23:22 ` prakash.sangappa
2018-05-08 0:05 ` Dave Hansen
2018-05-08 1:16 ` prakash.sangappa
2018-05-09 23:31 ` Dave Hansen
2018-09-12 20:42 ` prakash.sangappa
2018-09-12 20:57 ` prakash.sangappa
2018-09-14 1:33 ` Jann Horn
2018-09-14 6:21 ` Michal Hocko
2018-09-14 12:49 ` Jann Horn
2018-09-14 13:49 ` Michal Hocko
2018-09-14 18:07 ` Prakash Sangappa
2018-09-14 18:14 ` Jann Horn [this message]
2018-05-02 23:43 ` prakash.sangappa
2018-05-03 8:57 ` Michal Hocko
2018-05-03 22:37 ` prakash.sangappa
2018-05-04 11:10 ` Michal Hocko
2018-05-03 18:03 ` Christopher Lameter
2018-05-03 22:39 ` prakash.sangappa
2018-05-04 11:12 ` Michal Hocko
2018-05-04 16:18 ` Prakash Sangappa
2018-05-10 7:42 ` Michal Hocko
2018-05-10 16:00 ` Prakash Sangappa
2018-05-11 6:39 ` Michal Hocko
2018-05-04 14:57 ` Christopher Lameter
2018-05-04 16:27 ` Prakash Sangappa
2018-05-07 14:47 ` Christopher Lameter
2018-05-07 22:50 ` prakash.sangappa
2018-05-08 12:53 ` Christopher Lameter
2018-09-12 23:02 Alexey Dobriyan
2018-09-13 22:17 ` prakash.sangappa
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