From: Kees Cook <keescook@chromium.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Matthew Wilcox <willy@infradead.org>,
Cyril Hrubis <chrubis@suse.cz>, Michal Hocko <mhocko@kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Khalid Aziz <khalid.aziz@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King - ARM Linux <linux@armlinux.org.uk>,
Andrea Arcangeli <aarcange@redhat.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
Florian Weimer <fweimer@redhat.com>,
John Hubbard <jhubbard@nvidia.com>,
Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
Joel Stanley <joel@jms.id.au>, Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
Date: Thu, 7 Dec 2017 11:14:27 -0800 [thread overview]
Message-ID: <CAGXu5jLWRQn6EaXEEvdvXr+4gbiJawwp1EaLMfYisHVfMiqgSA@mail.gmail.com> (raw)
In-Reply-To: <87bmjbks4c.fsf@concordia.ellerman.id.au>
On Wed, Dec 6, 2017 at 9:46 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Matthew Wilcox <willy@infradead.org> writes:
>
>> On Tue, Dec 05, 2017 at 08:54:35PM -0800, Matthew Wilcox wrote:
>>> On Wed, Dec 06, 2017 at 03:51:44PM +1100, Michael Ellerman wrote:
>>> > Cyril Hrubis <chrubis@suse.cz> writes:
>>> >
>>> > > Hi!
>>> > >> > MAP_FIXED_UNIQUE
>>> > >> > MAP_FIXED_ONCE
>>> > >> > MAP_FIXED_FRESH
>>> > >>
>>> > >> Well, I can open a poll for the best name, but none of those you are
>>> > >> proposing sound much better to me. Yeah, naming sucks...
>>> > >
>>> > > Given that MAP_FIXED replaces the previous mapping MAP_FIXED_NOREPLACE
>>> > > would probably be a best fit.
>>> >
>>> > Yeah that could work.
>>> >
>>> > I prefer "no clobber" as I just suggested, because the existing
>>> > MAP_FIXED doesn't politely "replace" a mapping, it destroys the current
>>> > one - which you or another thread may be using - and clobbers it with
>>> > the new one.
>>>
>>> It's longer than MAP_FIXED_WEAK :-P
>>>
>>> You'd have to be pretty darn strong to clobber an existing mapping.
>>
>> I think we're thinking about this all wrong. We shouldn't document it as
>> "This is a variant of MAP_FIXED". We should document it as "Here's an
>> alternative to MAP_FIXED".
>>
>> So, just like we currently say "exactly one of MAP_SHARED or MAP_PRIVATE",
>> we could add a new paragraph saying "at most one of MAP_FIXED or
>> MAP_REQUIRED" and "any of the following values".
>>
>> Now, we should implement MAP_REQUIRED as having each architecture
>> define _MAP_NOT_A_HINT, and then #define MAP_REQUIRED (MAP_FIXED |
>> _MAP_NOT_A_HINT), but that's not information to confuse users with.
>>
>> Also, that lets us add a third option at some point that is Yet Another
>> Way to interpret the 'addr' argument, by having MAP_FIXED clear and
>> _MAP_NOT_A_HINT set.
>>
>> I'm not set on MAP_REQUIRED. I came up with some awful names
>> (MAP_TODDLER, MAP_TANTRUM, MAP_ULTIMATUM, MAP_BOSS, MAP_PROGRAM_MANAGER,
>> etc). But I think we should drop FIXED from the middle of the name.
>
> MAP_REQUIRED doesn't immediately grab me, but I don't actively dislike
> it either :)
>
> What about MAP_AT_ADDR ?
>
> It's short, and says what it does on the tin. The first argument to mmap
> is actually called "addr" too.
"FIXED" is supposed to do this too.
Pavel suggested:
MAP_ADD_FIXED
(which is different from "use fixed", and describes why it would fail:
can't add since it already exists.)
Perhaps "MAP_FIXED_NEW"?
There has been a request to drop "FIXED" from the name, so these:
MAP_FIXED_NOCLOBBER
MAP_FIXED_NOREPLACE
MAP_FIXED_ADD
MAP_FIXED_NEW
Could be:
MAP_NOCLOBBER
MAP_NOREPLACE
MAP_ADD
MAP_NEW
and we still have the unloved, but acceptable:
MAP_REQUIRED
My vote is still for "NOREPLACE" or "NOCLOBBER" since it's very
specific, though "NEW" is pretty clear too.
-Kees
--
Kees Cook
Pixel Security
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next prev parent reply other threads:[~2017-12-07 19:14 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-29 14:42 [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Michal Hocko
2017-11-29 14:42 ` [PATCH 1/2] " Michal Hocko
2017-12-06 5:15 ` Michael Ellerman
2017-12-06 9:27 ` Michal Hocko
2017-12-06 10:02 ` Michal Hocko
2017-12-07 12:07 ` Pavel Machek
2017-11-29 14:42 ` [PATCH 2/2] fs, elf: drop MAP_FIXED usage from elf_map Michal Hocko
2017-11-29 17:45 ` Khalid Aziz
2018-05-29 22:21 ` Mike Kravetz
2018-05-30 8:02 ` Michal Hocko
2018-05-30 15:00 ` Mike Kravetz
2018-05-30 16:25 ` Michal Hocko
2018-05-31 0:51 ` Mike Kravetz
2018-05-31 9:24 ` Michal Hocko
2018-05-31 21:46 ` Mike Kravetz
2017-11-29 14:45 ` [PATCH] mmap.2: document new MAP_FIXED_SAFE flag Michal Hocko
2017-11-30 3:16 ` John Hubbard
2017-11-30 8:23 ` Michal Hocko
2017-11-30 8:24 ` [PATCH v2] " Michal Hocko
2017-11-30 18:31 ` John Hubbard
2017-11-30 18:39 ` Michal Hocko
2017-11-29 15:13 ` [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Rasmus Villemoes
2017-11-29 15:50 ` Michal Hocko
2017-11-29 22:15 ` Kees Cook
2017-11-29 22:12 ` Kees Cook
2017-11-29 22:25 ` Kees Cook
2017-11-30 6:58 ` Michal Hocko
2017-12-01 15:26 ` Cyril Hrubis
2017-12-06 4:51 ` Michael Ellerman
2017-12-06 4:54 ` Matthew Wilcox
2017-12-06 7:03 ` Matthew Wilcox
2017-12-06 7:33 ` John Hubbard
2017-12-06 7:35 ` Florian Weimer
2017-12-06 8:06 ` John Hubbard
2017-12-06 8:54 ` Florian Weimer
2017-12-07 5:46 ` Michael Ellerman
2017-12-07 19:14 ` Kees Cook [this message]
2017-12-07 19:57 ` Matthew Wilcox
2017-12-08 8:33 ` Michal Hocko
2017-12-08 20:13 ` Kees Cook
2017-12-08 20:57 ` Matthew Wilcox
2017-12-08 11:08 ` Michael Ellerman
2017-12-08 14:27 ` Pavel Machek
2017-12-08 20:31 ` Cyril Hrubis
2017-12-08 20:47 ` Florian Weimer
2017-12-08 14:33 ` David Laight
2017-12-06 4:50 ` Michael Ellerman
2017-12-06 7:33 ` Rasmus Villemoes
2017-12-06 9:08 ` Michal Hocko
2017-12-07 0:19 ` Kees Cook
2017-12-07 1:08 ` John Hubbard
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