Hi all,
On Mon, Dec 10, 2018 at 9:15 AM Nicolas Boichat drinkcat@chromium.org wrote:
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:
- This series, adding support for GFP_DMA32 slab caches.
- genalloc, which requires pre-allocating the maximum number of L2 page tables (4096, so 4MB of memory).
- 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.
Does anyone have any further comment on this series? If not, which maintainer is going to pick this up? I assume Andrew Morton?
Thanks,
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