When unmapping a buffer from an IOMMU domain, the IOMMU framework unmaps
the buffer at a granule of the largest page size that is supported by
the IOMMU hardware and fits within the buffer. For every block that
is unmapped, the IOMMU framework will call into the IOMMU driver, and
then the io-pgtable framework to walk the page tables to find the entry
that corresponds to the IOVA, and then unmaps the entry.
This can be suboptimal in scenarios where a buffer or a piece of a
buffer can be split into several contiguous page blocks of the same size.
For example, consider an IOMMU that supports 4 KB page blocks, 2 MB page
blocks, and 1 GB page blocks, and a buffer that is 4 MB in size is being
unmapped at IOVA 0. The current call-flow will result in 4 indirect calls,
and 2 page table walks, to unmap 2 entries that are next to each other in
the page-tables, when both entries could have been unmapped in one shot
by clearing both page table entries in the same call.
The same optimization is applicable to mapping buffers as well, so
these patches implement a set of callbacks called unmap_pages and
map_pages to the io-pgtable code and IOMMU drivers which unmaps or maps
an IOVA range that consists of a number of pages of the same
page size that is supported by the IOMMU hardware, and allows for
manipulating multiple page table entries in the same set of indirect
calls. The reason for introducing these callbacks is to give other IOMMU
drivers/io-pgtable formats time to change to using the new callbacks, so
that the transition to using this approach can be done piecemeal.
Changes since V2:
* Added a check in __iommu_map() to check for the existence
of either the map or map_pages callback as per Lu's suggestion.
Changes since V1:
* Implemented the map_pages() callbacks
* Integrated Will's patches into this series which
address several concerns about how iommu_pgsize() partitioned a
buffer (I made a minor change to the patch which changes
iommu_pgsize() to use bitmaps by using the ULL variants of
the bitops)
Isaac J. Manjarres (9):
iommu/io-pgtable: Introduce unmap_pages() as a page table op
iommu: Add an unmap_pages() op for IOMMU drivers
iommu/io-pgtable: Introduce map_pages() as a page table op
iommu: Add a map_pages() op for IOMMU drivers
iommu: Add support for the map_pages() callback
iommu/io-pgtable-arm: Implement arm_lpae_unmap_pages()
iommu/io-pgtable-arm: Implement arm_lpae_map_pages()
iommu/arm-smmu: Implement the unmap_pages() IOMMU driver callback
iommu/arm-smmu: Implement the map_pages() IOMMU driver callback
Will Deacon (3):
iommu: Use bitmap to calculate page size in iommu_pgsize()
iommu: Split 'addr_merge' argument to iommu_pgsize() into separate
parts
iommu: Hook up '->unmap_pages' driver callback
drivers/iommu/arm/arm-smmu/arm-smmu.c | 38 +++++
drivers/iommu/io-pgtable-arm.c | 219 ++++++++++++++++++++++----
drivers/iommu/iommu.c | 130 +++++++++++----
include/linux/io-pgtable.h | 8 +
include/linux/iommu.h | 9 ++
5 files changed, 344 insertions(+), 60 deletions(-)
--
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