[PATCH v6 0/6] DMA mapping changes for SCSI core

John Garry
2022-07-14T11:22:23Z

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/

Changes since v5:
- Rebase to Linux 5.19-rc6
- Add Martin's tags to unmodified patches (thanks!)
- Apply DMA opt limit to max_sectors in sd driver, and not max_hw_sectors

Changes since v4:
- tweak libata and other patch titles
- Add Robin's tag (thanks!)
- Clarify description of new DMA mapping API

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

John Garry (6):
dma-mapping: Add dma_opt_mapping_size()
dma-iommu: Add iommu_dma_opt_mapping_size()
scsi: core: Cap shost max_sectors according to DMA limits only once
scsi: sd: Allow max_sectors be capped at DMA optimal size limit
scsi: scsi_transport_sas: Cap shost opt_sectors according to DMA
optimal limit
ata: libata-scsi: Cap ata_device->max_sectors according to
shost->max_sectors

Documentation/core-api/dma-api.rst | 14 ++++++++++++++
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 ++++++
drivers/scsi/sd.c | 2 ++
include/linux/dma-map-ops.h | 1 +
include/linux/dma-mapping.h | 5 +++++
include/linux/iova.h | 2 ++
include/scsi/scsi_host.h | 1 +
kernel/dma/mapping.c | 12 ++++++++++++
13 files changed, 60 insertions(+), 4 deletions(-)

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2.35.3