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Will Deacon authored
Commit add02cfd ("iommu: Introduce Interface for IOMMU TLB Flushing") added three new TLB flushing operations to the IOMMU API so that the underlying driver operations can be batched when unmapping large regions of IO virtual address space. However, the ->iotlb_range_add() callback has not been implemented by any IOMMU drivers (amd_iommu.c implements it as an empty function, which incurs the overhead of an indirect branch). Instead, drivers either flush the entire IOTLB in the ->iotlb_sync() callback or perform the necessary invalidation during ->unmap(). Attempting to implement ->iotlb_range_add() for arm-smmu-v3.c revealed two major issues: 1. The page size used to map the region in the page-table is not known, and so it is not generally possible to issue TLB flushes in the most efficient manner. 2. The only mutable state passed to the callback is a pointer to the iommu_domain, which can be accessed concurrently and therefore requires expensive synchronisation to keep track of the outstanding flushes. Remove the callback entirely in preparation for extending ->unmap() and ->iotlb_sync() to update a token on the caller's stack. Signed-off-by: Will Deacon <will@kernel.org>
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