From: John Hubbard <jhubbard@nvidia.com>
To: Michal Hocko <mhocko@kernel.org>,
Michael Kerrisk <mtk.manpages@gmail.com>
Cc: linux-api@vger.kernel.org, Khalid Aziz <khalid.aziz@oracle.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King - ARM Linux <linux@armlinux.org.uk>,
Andrea Arcangeli <aarcange@redhat.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Florian Weimer <fweimer@redhat.com>
Subject: Re: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag
Date: Thu, 30 Nov 2017 10:31:12 -0800 [thread overview]
Message-ID: <1a96e274-a986-12b7-6e47-fc6355cbf637@nvidia.com> (raw)
In-Reply-To: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz>
On 11/30/2017 12:24 AM, Michal Hocko wrote:
> Updated version based on feedback from John.
> ---
> From ade1eba229b558431581448e7d7838f0e1fe2c49 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Wed, 29 Nov 2017 15:32:08 +0100
> Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag
>
> 4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows the caller to
> atomicaly probe for a given address range.
>
> [wording heavily updated by John Hubbard <jhubbard@nvidia.com>]
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> man2/mmap.2 | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/man2/mmap.2 b/man2/mmap.2
> index 385f3bfd5393..923bbb290875 100644
> --- a/man2/mmap.2
> +++ b/man2/mmap.2
> @@ -225,6 +225,22 @@ will fail.
> Because requiring a fixed address for a mapping is less portable,
> the use of this option is discouraged.
> .TP
> +.BR MAP_FIXED_SAFE " (since Linux 4.16)"
> +Similar to MAP_FIXED with respect to the
> +.I
> +addr
> +enforcement, but different in that MAP_FIXED_SAFE never clobbers a pre-existing
> +mapped range. If the requested range would collide with an existing
> +mapping, then this call fails with
> +.B EEXIST.
> +This flag can therefore be used as a way to atomically (with respect to other
> +threads) attempt to map an address range: one thread will succeed; all others
> +will report failure. Please note that older kernels which do not recognize this
> +flag will typically (upon detecting a collision with a pre-existing mapping)
> +fall back a "non-MAP_FIXED" type of behavior: they will return an address that
...and now I've created my own typo: please make that "fall back to a" (the
"to" was missing).
Sorry about the churn. It turns out that the compiler doesn't catch these. :)
thanks,
John Hubbard
> +is different than the requested one. Therefore, backward-compatible software
> +should check the returned address against the requested address.
> +.TP
> .B MAP_GROWSDOWN
> This flag is used for stacks.
> It indicates to the kernel virtual memory system that the mapping
> @@ -449,6 +465,12 @@ is not a valid file descriptor (and
> .B MAP_ANONYMOUS
> was not set).
> .TP
> +.B EEXIST
> +range covered by
> +.IR addr ,
> +.IR length
> +is clashing with an existing mapping.
> +.TP
> .B EINVAL
> We don't like
> .IR addr ,
>
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next prev parent reply other threads:[~2017-11-30 18:31 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 [this message]
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
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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