From: Liam Howlett <liam.howlett@oracle.com>
To: Suren Baghdasaryan <surenb@google.com>
Cc: "John Hubbard" <jhubbard@nvidia.com>,
"Kees Cook" <keescook@chromium.org>,
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Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting
Date: Fri, 8 Oct 2021 01:04:32 +0000 [thread overview]
Message-ID: <20211008010425.atn6kzho7xmnet4a@revolver> (raw)
In-Reply-To: <CAJuCfpHJmDeyTXdsO8T5tTLgcNT22b15hj41EBNCDXBAoCdpog@mail.gmail.com>
* Suren Baghdasaryan <surenb@google.com> [211007 17:32]:
> On Thu, Oct 7, 2021 at 12:03 PM 'John Hubbard' via kernel-team
> <kernel-team@android.com> wrote:
> >
> > On 10/7/21 11:50, Suren Baghdasaryan wrote:
> > ...
> > >>>>>>>>>> I believe Pavel meant something as simple as
> > >>>>>>>>>> $ YOUR_FILE=$YOUR_IDS_DIR/my_string_name
> > >>>>>>>>>> $ touch $YOUR_FILE
> > >>>>>>>>>> $ stat -c %i $YOUR_FILE
> > >>>>>>>
> > >>>>>>> Ah, ok, now I understand the proposal. Thanks for the clarification!
> > >>>>>>> So, this would use filesystem as a directory for inode->name mappings.
> > >>>>>>> One rough edge for me is that the consumer would still need to parse
> > >>>>>>> /proc/$pid/maps and convert [anon:inode] into [anon:name] instead of
> > >>>>>>> just dumping the content for the user. Would it be acceptable if we
> > >>>>>>> require the ID provided by prctl() to always be a valid inode and
> > >>>>>>> show_map_vma() would do the inode-to-filename conversion when
> > >>>>>>> generating maps/smaps files? I know that inode->dentry is not
> > >>>>>>> one-to-one mapping but we can simply output the first dentry name.
> > >>>>>>> WDYT?
> > >>>>>>
> > >>>>>> No. You do not want to dictate any particular way of the mapping. The
> > >>>>>> above is just one way to do that without developing any actual mapping
> > >>>>>> yourself. You just use a filesystem for that. Kernel doesn't and
> > >>>>>> shouldn't understand the meaning of those numbers. It has no business in
> > >>>>>> that.
> > >>>>>>
> > >>>>>> In a way this would be pushing policy into the kernel.
> > >>>>>
> > >>>>> I can see your point. Any other ideas on how to prevent tools from
> > >>>>> doing this id-to-name conversion themselves?
> > >>>>
> > >>>> I really fail to understand why you really want to prevent them from that.
> > >>>> Really, the whole thing is just a cookie that kernel maintains for memory
> > >>>> mappings so that two parties can understand what the meaning of that
> > >>>> mapping is from a higher level. They both have to agree on the naming
> > >>>> but the kernel shouldn't dictate any specific convention because the
> > >>>> kernel _doesn't_ _care_. These things are not really anything actionable
> > >>>> for the kernel. It is just a metadata.
> > >>>
> > >>> The desire is for one of these two parties to be a human who can get
> > >>> the data and use it as is without additional conversions.
> > >>> /proc/$pid/maps could report FD numbers instead of pathnames, which
> > >>> could be converted to pathnames in userspace. However we do not do
> > >>> that because pathnames are more convenient for humans to identify a
> > >>> specific resource. Same logic applies here IMHO.
> > >>
> > >> Yes, please. It really seems like the folks that are interested in this
> > >> feature want strings. (I certainly do.) For those not interested in the
> > >> feature, it sounds like a CONFIG to keep it away would be sufficient.
> > >> Can we just move forward with that?
> > >
> > > Would love to if others are ok with this.
> > >
> >
> > If this doesn't get accepted, then another way forward would to continue
> > the ideas above to their logical conclusion, and create a new file system:
> > vma-fs. Like debug-fs and other special file systems, similar policy and
> > motivation. Also protected by a CONFIG option.
>
> TBH, I would prefer to have the current simple solution protected with
> a CONFIG option.
>
> >
> > Actually this seems at least as natural as the procfs approach, especially
> > given the nature of these strings, which feel more like dir+file names, than
> > simple strings.
I think the current locking around VMAs makes this a very tricky, if not
impossible, path. Watching a proc file which takes the mmap_lock() is
painful enough. Considering how hard it has been to have this feature
added, I cannot see locking changes being accepted as a more feasible
approach nor can I see increased mmap_lock() contention from any feature
being desired.
I like the CONFIG option. The patches are in good shape and have a
clever way around the (unlikely?) scalability issue that existed.
Thanks,
Liam
next prev parent reply other threads:[~2021-10-08 1:05 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 20:56 [PATCH v10 1/3] mm: rearrange madvise code to allow for reuse Suren Baghdasaryan
2021-10-01 20:56 ` [PATCH v10 2/3] mm: add a field to store names for private anonymous memory Suren Baghdasaryan
2021-10-01 23:08 ` Andrew Morton
2021-10-02 0:52 ` Suren Baghdasaryan
2021-10-04 16:21 ` Suren Baghdasaryan
2021-10-07 2:39 ` Andrew Morton
2021-10-07 2:50 ` Suren Baghdasaryan
2021-10-01 20:56 ` [PATCH v10 3/3] mm: add anonymous vma name refcounting Suren Baghdasaryan
2021-10-05 18:42 ` Pavel Machek
2021-10-05 19:14 ` Suren Baghdasaryan
2021-10-05 19:21 ` Kees Cook
2021-10-05 20:04 ` Pavel Machek
2021-10-05 20:43 ` Suren Baghdasaryan
2021-10-06 6:57 ` John Hubbard
2021-10-06 8:27 ` Michal Hocko
2021-10-06 9:27 ` David Hildenbrand
2021-10-06 15:01 ` Suren Baghdasaryan
2021-10-06 15:07 ` David Hildenbrand
2021-10-06 15:20 ` Suren Baghdasaryan
2021-10-07 2:29 ` Andrew Morton
2021-10-07 2:46 ` Suren Baghdasaryan
2021-10-07 2:53 ` Andrew Morton
2021-10-07 3:01 ` Suren Baghdasaryan
2021-10-07 7:27 ` David Hildenbrand
2021-10-07 7:33 ` David Hildenbrand
2021-10-07 15:42 ` Suren Baghdasaryan
2021-10-06 17:58 ` Pavel Machek
2021-10-06 18:18 ` Suren Baghdasaryan
2021-10-07 8:10 ` Michal Hocko
2021-10-07 8:41 ` Pavel Machek
2021-10-07 8:47 ` Rasmus Villemoes
2021-10-07 10:15 ` Pavel Machek
2021-10-07 16:04 ` Suren Baghdasaryan
2021-10-07 16:40 ` Michal Hocko
2021-10-07 16:58 ` Suren Baghdasaryan
2021-10-07 17:31 ` Michal Hocko
2021-10-07 17:50 ` Suren Baghdasaryan
2021-10-07 18:12 ` Kees Cook
2021-10-07 18:50 ` Suren Baghdasaryan
2021-10-07 19:02 ` John Hubbard
2021-10-07 21:32 ` Suren Baghdasaryan
2021-10-08 1:04 ` Liam Howlett [this message]
2021-10-08 7:25 ` Rasmus Villemoes
2021-10-08 7:43 ` David Hildenbrand
2021-10-08 21:13 ` Kees Cook
2021-10-08 6:34 ` Michal Hocko
2021-10-08 14:14 ` Dave Hansen
2021-10-08 14:57 ` Michal Hocko
2021-10-08 16:10 ` Suren Baghdasaryan
2021-10-08 20:58 ` Kees Cook
2021-10-11 8:36 ` Michal Hocko
2021-10-12 1:18 ` Suren Baghdasaryan
2021-10-12 1:20 ` Suren Baghdasaryan
2021-10-12 3:00 ` Johannes Weiner
2021-10-12 5:36 ` Suren Baghdasaryan
2021-10-12 18:26 ` Johannes Weiner
2021-10-12 18:52 ` Suren Baghdasaryan
2021-10-12 20:41 ` Johannes Weiner
2021-10-12 20:59 ` Suren Baghdasaryan
2021-10-12 7:36 ` Michal Hocko
2021-10-12 16:50 ` Suren Baghdasaryan
2021-10-12 7:43 ` David Hildenbrand
2021-10-12 17:01 ` Suren Baghdasaryan
2021-10-14 20:16 ` Suren Baghdasaryan
2021-10-15 8:03 ` David Hildenbrand
2021-10-15 16:30 ` Suren Baghdasaryan
2021-10-15 16:39 ` David Hildenbrand
2021-10-15 18:33 ` Suren Baghdasaryan
2021-10-15 17:45 ` Kees Cook
2021-10-07 7:59 ` Michal Hocko
2021-10-07 15:45 ` Suren Baghdasaryan
2021-10-07 16:37 ` Michal Hocko
2021-10-07 16:43 ` Suren Baghdasaryan
2021-10-07 17:25 ` Michal Hocko
2021-10-07 17:30 ` Suren Baghdasaryan
2021-10-04 7:03 ` [PATCH v10 1/3] mm: rearrange madvise code to allow for reuse Rolf Eike Beer
2021-10-04 16:18 ` Suren Baghdasaryan
2021-10-05 21:00 ` Liam Howlett
2021-10-05 21:30 ` Suren Baghdasaryan
2021-10-06 17:33 ` Liam Howlett
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