From: Michael Ellerman <mpe@ellerman.id.au>
To: Matthew Wilcox <willy@infradead.org>, Kees Cook <keescook@chromium.org>
Cc: 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: Fri, 08 Dec 2017 22:08:07 +1100 [thread overview]
Message-ID: <87shclh3zc.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20171207195727.GA26792@bombadil.infradead.org>
Matthew Wilcox <willy@infradead.org> writes:
> On Thu, Dec 07, 2017 at 11:14:27AM -0800, Kees Cook wrote:
>> On Wed, Dec 6, 2017 at 9:46 PM, Michael Ellerman <mpe@ellerman.id.au> wrote:
>> > Matthew Wilcox <willy@infradead.org> writes:
>> >> 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".
>> >
>> > 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.
>
> How about MAP_NOFORCE?
It doesn't tell me that addr is not a hint. That's a crucial detail.
Without MAP_FIXED mmap never "forces/replaces/clobbers", so why would I
need MAP_NOFORCE if I don't have MAP_FIXED?
So it needs something in there to indicate that the addr is not a hint,
that's the only thing that flag actually *does*.
If we had a time machine, the right set of flags would be:
- MAP_FIXED: don't treat addr as a hint, fail if addr is not free
- MAP_REPLACE: replace an existing mapping (or force or clobber)
But the two were conflated for some reason in the current MAP_FIXED.
Given we can't go back and fix it, the closest we can get is to add a
variant of MAP_FIXED which subtracts the "REPLACE" semantic.
ie: MAP_FIXED_NOREPLACE
cheers
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next prev parent reply other threads:[~2017-12-08 11:08 UTC|newest]
Thread overview: 44+ 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
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
[not found] ` <b154b794-7a8b-995e-0954-9234b9446b31-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
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
[not found] ` <CAGXu5jLa=b2HhjWXXTQunaZuz11qUhm5aNXHpS26jVqb=G-gfw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
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
[not found] ` <5f4fc834-274a-b8f1-bda0-5bcddc5902ed-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06 7:35 ` Florian Weimer
2017-12-06 8:06 ` John Hubbard
[not found] ` <27ee1755-76d8-f086-5760-9c973b31108a-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06 8:54 ` Florian Weimer
[not found] ` <20171206070355.GA32044-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2017-12-07 5:46 ` Michael Ellerman
2017-12-07 19:14 ` Kees Cook
[not found] ` <CAGXu5jLWRQn6EaXEEvdvXr+4gbiJawwp1EaLMfYisHVfMiqgSA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-07 19:57 ` Matthew Wilcox
2017-12-08 8:33 ` Michal Hocko
[not found] ` <20171208083315.GR20234-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-12-08 20:13 ` Kees Cook
[not found] ` <CAGXu5j+VupGmKEEHx-uNXw27Xvndu=0ObsBqMwQiaYPyMGD+vw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-08 20:57 ` Matthew Wilcox
2017-12-08 11:08 ` Michael Ellerman [this message]
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
[not found] ` <87zi6we9z2.fsf-W0DJWXSxmBNbyGPkN3NxC2scP1bn1w/D@public.gmane.org>
2017-12-06 7:33 ` Rasmus Villemoes
[not found] ` <a3b3129a-2626-a65e-59b0-68aada523723-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
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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