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[v4,0/5] DMA mapping changes for SCSI core

Message ID 1656343521-62897-1-git-send-email-john.garry@huawei.com
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Series DMA mapping changes for SCSI core | expand

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John Garry June 27, 2022, 3:25 p.m. UTC 
As reported in [0], DMA mappings whose size exceeds the IOMMU IOVA caching
limit may see a big performance hit.

This series introduces a new DMA mapping API, dma_opt_mapping_size(), so
that drivers may know this limit when performance is a factor in the
mapping.

The SCSI SAS transport code is modified only to use this limit. For now I
did not want to touch other hosts as I have a concern that this change
could cause a performance regression.

I also added a patch for libata-scsi as it does not currently honour the
shost max_sectors limit.

[0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@huawei.com/
[1] https://lore.kernel.org/linux-iommu/f5b78c9c-312e-70ab-ecbb-f14623a4b6e3@arm.com/

Changes since v3:
- Apply max DMA optimial limit to SAS hosts only
  Note: Even though "scsi: core: Cap shost max_sectors only once when
  adding" is a subset of a previous patch I did not transfer the RB tags
- Rebase on v5.19-rc4

Changes since v2:
- Rebase on v5.19-rc1
- Add Damien's tag to 2/4 (thanks)

Changes since v1:
- Relocate scsi_add_host_with_dma() dma_dev check (Reported by Dan)
- Add tags from Damien and Martin (thanks)
  - note: I only added Martin's tag to the SCSI patch

John Garry (5):
  dma-mapping: Add dma_opt_mapping_size()
  dma-iommu: Add iommu_dma_opt_mapping_size()
  scsi: core: Cap shost max_sectors according to DMA mapping limits only
    once
  scsi: scsi_transport_sas: Cap shost max_sectors according to DMA
    optimal mapping limit
  libata-scsi: Cap ata_device->max_sectors according to
    shost->max_sectors

 Documentation/core-api/dma-api.rst |  9 +++++++++
 drivers/ata/libata-scsi.c          |  1 +
 drivers/iommu/dma-iommu.c          |  6 ++++++
 drivers/iommu/iova.c               |  5 +++++
 drivers/scsi/hosts.c               |  5 +++++
 drivers/scsi/scsi_lib.c            |  4 ----
 drivers/scsi/scsi_transport_sas.c  |  6 ++++++
 include/linux/dma-map-ops.h        |  1 +
 include/linux/dma-mapping.h        |  5 +++++
 include/linux/iova.h               |  2 ++
 kernel/dma/mapping.c               | 12 ++++++++++++
 11 files changed, 52 insertions(+), 4 deletions(-)