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* [PATCH v6 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables
@ 2018-12-10  1:15 Nicolas Boichat
  2018-12-10  1:15 ` [PATCH v6 1/3] mm: Add support for kmem caches in DMA32 zone Nicolas Boichat
                   ` (3 more replies)
  0 siblings, 4 replies; 13+ messages in thread
From: Nicolas Boichat @ 2018-12-10  1:15 UTC (permalink / raw)
  To: Will Deacon
  Cc: Michal Hocko, Levin Alexander, linux-mm, Christoph Lameter,
	Huaisheng Ye, Joerg Roedel, Matthew Wilcox, hch,
	linux-arm-kernel, David Rientjes, yingjoe.chen, Vlastimil Babka,
	Tomasz Figa, Mike Rapoport, hsinyi, Matthias Brugger,
	Joonsoo Kim, Yong Wu, Robin Murphy, linux-kernel, stable,
	Pekka Enberg, iommu, Andrew Morton, Mel Gorman

This is a follow-up to the discussion in [1], [2].

IOMMUs using ARMv7 short-descriptor format require page tables
(level 1 and 2) to be allocated within the first 4GB of RAM, even
on 64-bit systems.

For L1 tables that are bigger than a page, we can just use __get_free_pages
with GFP_DMA32 (on arm64 systems only, arm would still use GFP_DMA).

For L2 tables that only take 1KB, it would be a waste to allocate a full
page, so we considered 3 approaches:
 1. This series, adding support for GFP_DMA32 slab caches.
 2. genalloc, which requires pre-allocating the maximum number of L2 page
    tables (4096, so 4MB of memory).
 3. page_frag, which is not very memory-efficient as it is unable to reuse
    freed fragments until the whole page is freed. [3]

This series is the most memory-efficient approach.

stable@ note:
  We confirmed that this is a regression, and IOMMU errors happen on 4.19
  and linux-next/master on MT8173 (elm, Acer Chromebook R13). The issue
  most likely starts from commit ad67f5a6545f ("arm64: replace ZONE_DMA
  with ZONE_DMA32"), i.e. 4.15, and presumably breaks a number of Mediatek
  platforms (and maybe others?).

[1] https://lists.linuxfoundation.org/pipermail/iommu/2018-November/030876.html
[2] https://lists.linuxfoundation.org/pipermail/iommu/2018-December/031696.html
[3] https://patchwork.codeaurora.org/patch/671639/

Changes since v1:
 - Add support for SLAB_CACHE_DMA32 in slab and slub (patches 1/2)
 - iommu/io-pgtable-arm-v7s (patch 3):
   - Changed approach to use SLAB_CACHE_DMA32 added by the previous
     commit.
   - Use DMA or DMA32 depending on the architecture (DMA for arm,
     DMA32 for arm64).

Changes since v2:
 - Reworded and expanded commit messages
 - Added cache_dma32 documentation in PATCH 2/3.

v3 used the page_frag approach, see [3].

Changes since v4:
 - Dropped change that removed GFP_DMA32 from GFP_SLAB_BUG_MASK:
   instead we can just call kmem_cache_*alloc without GFP_DMA32
   parameter. This also means that we can drop PATCH v4 1/3, as we
   do not make any changes in GFP flag verification.
 - Dropped hunks that added cache_dma32 sysfs file, and moved
   the hunks to PATCH v5 3/3, so that maintainer can decide whether
   to pick the change independently.

Changes since v5:
 - Rename ARM_V7S_TABLE_SLAB_CACHE to ARM_V7S_TABLE_SLAB_FLAGS.
 - Add stable@ to cc.

Nicolas Boichat (3):
  mm: Add support for kmem caches in DMA32 zone
  iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging
  mm: Add /sys/kernel/slab/cache/cache_dma32

 Documentation/ABI/testing/sysfs-kernel-slab |  9 +++++++++
 drivers/iommu/io-pgtable-arm-v7s.c          | 19 +++++++++++++++----
 include/linux/slab.h                        |  2 ++
 mm/slab.c                                   |  2 ++
 mm/slab.h                                   |  3 ++-
 mm/slab_common.c                            |  2 +-
 mm/slub.c                                   | 16 ++++++++++++++++
 tools/vm/slabinfo.c                         |  7 ++++++-
 8 files changed, 53 insertions(+), 7 deletions(-)

-- 
2.20.0.rc2.403.gdbc3b29805-goog


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Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-12-10  1:15 [PATCH v6 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables Nicolas Boichat
2018-12-10  1:15 ` [PATCH v6 1/3] mm: Add support for kmem caches in DMA32 zone Nicolas Boichat
2018-12-10  1:15 ` [PATCH v6 2/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging Nicolas Boichat
2018-12-10 15:35   ` Will Deacon
2019-01-19 23:57   ` Will Deacon
2018-12-10  1:15 ` [PATCH v6 3/3] mm: Add /sys/kernel/slab/cache/cache_dma32 Nicolas Boichat
     [not found] ` <CANMq1KAmFKpcxi49wJyfP4N01A80B2d-2RGY2Wrwg0BvaFxAxg@mail.gmail.com>
2019-01-11 10:21   ` [PATCH v6 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables Joerg Roedel
2019-01-22 22:51     ` Nicolas Boichat
2019-02-13 17:12       ` Vlastimil Babka
2019-02-25  0:23         ` Nicolas Boichat
2019-03-19  7:41           ` Nicolas Boichat
2019-03-19 17:56             ` Andrew Morton
2019-03-20  0:20               ` Nicolas Boichat

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