From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752106AbdK3SbP (ORCPT ); Thu, 30 Nov 2017 13:31:15 -0500 Received: from hqemgate14.nvidia.com ([216.228.121.143]:16642 "EHLO hqemgate14.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750964AbdK3SbN (ORCPT ); Thu, 30 Nov 2017 13:31:13 -0500 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Thu, 30 Nov 2017 10:31:12 -0800 Subject: Re: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag To: Michal Hocko , Michael Kerrisk CC: , Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , , LKML , , Florian Weimer References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> X-Nvconfidentiality: public From: John Hubbard Message-ID: <1a96e274-a986-12b7-6e47-fc6355cbf637@nvidia.com> Date: Thu, 30 Nov 2017 10:31:12 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> X-Originating-IP: [10.110.48.28] X-ClientProxiedBy: HQMAIL106.nvidia.com (172.18.146.12) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > 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 ] > Signed-off-by: Michal Hocko > --- > 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 , > From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Hubbard Subject: Re: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag Date: Thu, 30 Nov 2017 10:31:12 -0800 Message-ID: <1a96e274-a986-12b7-6e47-fc6355cbf637@nvidia.com> References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org To: Michal Hocko , Michael Kerrisk Cc: linux-api@vger.kernel.org, Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Florian Weimer List-Id: linux-api@vger.kernel.org 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 > 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 ] > Signed-off-by: Michal Hocko > --- > 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 , > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id B15386B0069 for ; Thu, 30 Nov 2017 13:31:14 -0500 (EST) Received: by mail-pl0-f71.google.com with SMTP id h1so3186448plh.23 for ; Thu, 30 Nov 2017 10:31:14 -0800 (PST) Received: from hqemgate14.nvidia.com (hqemgate14.nvidia.com. [216.228.121.143]) by mx.google.com with ESMTPS id v8si3576994plp.37.2017.11.30.10.31.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Nov 2017 10:31:13 -0800 (PST) Subject: Re: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> From: John Hubbard Message-ID: <1a96e274-a986-12b7-6e47-fc6355cbf637@nvidia.com> Date: Thu, 30 Nov 2017 10:31:12 -0800 MIME-Version: 1.0 In-Reply-To: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Michael Kerrisk Cc: linux-api@vger.kernel.org, Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Florian Weimer 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 > 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 ] > Signed-off-by: Michal Hocko > --- > 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 , > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org