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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: linux-arch@vger.kernel.org,
	Linus Torvalds <torvalds@linuxfoundation.org>,
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	"David S. Miller" <davem@davemloft.net>,
	sparclinux@vger.kernel.org
Subject: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends
Date: Sat, 19 Sep 2020 11:17:51 +0200
Message-ID: <20200919091751.011116649@linutronix.de> (raw)

First of all, sorry for the horribly big Cc list!

Following up to the discussion in:

  https://lore.kernel.org/r/20200914204209.256266093@linutronix.de

this provides a preemptible variant of kmap_atomic & related
interfaces. This is achieved by:

 - Consolidating all kmap atomic implementations in generic code

 - Switching from per CPU storage of the kmap index to a per task storage

 - Adding a pteval array to the per task storage which contains the ptevals
   of the currently active temporary kmaps

 - Adding context switch code which checks whether the outgoing or the
   incoming task has active temporary kmaps. If so, the outgoing task's
   kmaps are removed and the incoming task's kmaps are restored.

 - Adding new interfaces k[un]map_temporary*() which are not disabling
   preemption and can be called from any context (except NMI).

   Contrary to kmap() which provides preemptible and "persistant" mappings,
   these interfaces are meant to replace the temporary mappings provided by
   kmap_atomic*() today.

This allows to get rid of conditional mapping choices and allows to have
preemptible short term mappings on 64bit which are today enforced to be
non-preemptible due to the highmem constraints. It clearly puts overhead on
the highmem users, but highmem is slow anyway.

This is not a wholesale conversion which makes kmap_atomic magically
preemptible because there might be usage sites which rely on the implicit
preempt disable. So this needs to be done on a case by case basis and the
call sites converted to kmap_temporary.

Note, that this is only lightly tested on X86 and completely untested on
all other architectures.

The lot is also available from

   git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git highmem

Thanks,

	tglx
---
 a/arch/arm/mm/highmem.c               |  121 ---------------------
 a/arch/microblaze/mm/highmem.c        |   78 -------------
 a/arch/nds32/mm/highmem.c             |   48 --------
 a/arch/powerpc/mm/highmem.c           |   67 -----------
 a/arch/sparc/mm/highmem.c             |  115 --------------------
 arch/arc/Kconfig                      |    1 
 arch/arc/include/asm/highmem.h        |    8 +
 arch/arc/mm/highmem.c                 |   44 -------
 arch/arm/Kconfig                      |    1 
 arch/arm/include/asm/highmem.h        |   30 +++--
 arch/arm/mm/Makefile                  |    1 
 arch/csky/Kconfig                     |    1 
 arch/csky/include/asm/highmem.h       |    4 
 arch/csky/mm/highmem.c                |   75 -------------
 arch/microblaze/Kconfig               |    1 
 arch/microblaze/include/asm/highmem.h |    6 -
 arch/microblaze/mm/Makefile           |    1 
 arch/microblaze/mm/init.c             |    6 -
 arch/mips/Kconfig                     |    1 
 arch/mips/include/asm/highmem.h       |    4 
 arch/mips/mm/highmem.c                |   77 -------------
 arch/mips/mm/init.c                   |    3 
 arch/nds32/Kconfig.cpu                |    1 
 arch/nds32/include/asm/highmem.h      |   21 ++-
 arch/nds32/mm/Makefile                |    1 
 arch/powerpc/Kconfig                  |    1 
 arch/powerpc/include/asm/highmem.h    |    6 -
 arch/powerpc/mm/Makefile              |    1 
 arch/powerpc/mm/mem.c                 |    7 -
 arch/sparc/Kconfig                    |    1 
 arch/sparc/include/asm/highmem.h      |    7 -
 arch/sparc/mm/Makefile                |    3 
 arch/sparc/mm/srmmu.c                 |    2 
 arch/x86/include/asm/fixmap.h         |    1 
 arch/x86/include/asm/highmem.h        |   12 +-
 arch/x86/include/asm/iomap.h          |   29 +++--
 arch/x86/mm/highmem_32.c              |   59 ----------
 arch/x86/mm/init_32.c                 |   15 --
 arch/x86/mm/iomap_32.c                |   57 ----------
 arch/xtensa/Kconfig                   |    1 
 arch/xtensa/include/asm/highmem.h     |    9 +
 arch/xtensa/mm/highmem.c              |   44 -------
 b/arch/x86/Kconfig                    |    3 
 include/linux/highmem.h               |  141 +++++++++++++++---------
 include/linux/io-mapping.h            |    2 
 include/linux/sched.h                 |    9 +
 kernel/sched/core.c                   |   10 +
 mm/Kconfig                            |    3 
 mm/highmem.c                          |  192 ++++++++++++++++++++++++++++++++--
 49 files changed, 422 insertions(+), 909 deletions(-)

             reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-19  9:17 Thomas Gleixner [this message]
2020-09-19  9:17 ` [patch RFC 01/15] mm/highmem: Un-EXPORT __kmap_atomic_idx() Thomas Gleixner
2020-09-21  6:23   ` Christoph Hellwig
2020-09-19  9:17 ` [patch RFC 02/15] highmem: Provide generic variant of kmap_atomic* Thomas Gleixner
2020-09-21  6:28   ` Christoph Hellwig
2020-09-19  9:17 ` [patch RFC 03/15] x86/mm/highmem: Use generic kmap atomic implementation Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 04/15] arc/mm/highmem: " Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 05/15] ARM: highmem: Switch to generic kmap atomic Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 06/15] csky/mm/highmem: " Thomas Gleixner
2020-09-23  0:05   ` Guo Ren
2020-09-19  9:17 ` [patch RFC 07/15] microblaze/mm/highmem: " Thomas Gleixner
2020-09-19  9:17 ` [patch RFC 08/15] mips/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 09/15] nds32/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 10/15] powerpc/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 11/15] sparc/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 12/15] xtensa/mm/highmem: " Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 13/15] mm/highmem: Remove the old kmap_atomic cruft Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 14/15] sched: highmem: Store temporary kmaps in task struct Thomas Gleixner
2020-09-19  9:18 ` [patch RFC 15/15] mm/highmem: Provide kmap_temporary* Thomas Gleixner
2020-09-19 10:35 ` [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Daniel Vetter
2020-09-19 10:37   ` Daniel Vetter
2020-09-20  6:23     ` Thomas Gleixner
2020-09-20  8:23       ` Daniel Vetter
2020-09-20 17:24         ` Thomas Gleixner
2020-09-19 17:18 ` Linus Torvalds
2020-09-19 17:39   ` Matthew Wilcox
2020-09-19 19:13     ` Linus Torvalds
2020-09-21 19:58     ` Ira Weiny
2020-09-20  6:41   ` Thomas Gleixner
2020-09-20  8:49     ` Thomas Gleixner
2020-09-20 16:57       ` Linus Torvalds
2020-09-20 17:40         ` Thomas Gleixner
2020-09-20 17:42           ` Linus Torvalds
2020-09-20 17:58             ` Linus Torvalds
2020-09-21  7:39             ` Thomas Gleixner
2020-09-21 16:24               ` Linus Torvalds
2020-09-21 19:27                 ` Thomas Gleixner
2020-09-23  8:40                   ` peterz
2020-09-23 13:35                     ` Thomas Gleixner
2020-09-23 15:52                     ` Steven Rostedt
2020-09-23 20:55                       ` Thomas Gleixner
2020-09-23 21:12                         ` Steven Rostedt
2020-09-24  6:57                           ` Thomas Gleixner
2020-09-24 12:32                             ` Steven Rostedt
2020-09-24 12:42                               ` Peter Zijlstra
2020-09-24 13:51                                 ` Steven Rostedt
2020-09-24 13:58                                   ` Peter Zijlstra
2020-09-24 17:55                               ` Thomas Gleixner
2020-09-24 18:58                                 ` Steven Rostedt
2020-09-24  8:27                       ` peterz
2020-09-24 19:36                         ` Daniel Bristot de Oliveira
2020-09-23 10:19                   ` peterz
2020-09-23 12:33                     ` Thomas Gleixner
2020-09-23 14:33                   ` Thomas Gleixner

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