linux/kernel/dma, branch v6.16

dma-contiguous: hornor the cma address limit setup by user

2025-06-12T06:38:40Z

When porting a cma related usage from x86_64 server to arm64 server, the "cma=4G@4G" setup failed on arm64. The reason is arm64 and some other architectures have specific physical address limit for reserved cma area, like 4GB due to the device's need for 32 bit dma. Actually lots of platforms of those architectures don't have this device dma limit, but still have to obey it, and are not able to reserve a huge cma pool. This situation could be improved by honoring the user input cma physical address than the arch limit. As when users specify it, they already knows what the default is which probably can't suit them. Suggested-by: Robin Murphy Signed-off-by: Feng Tang Signed-off-by: Marek Szyprowski Link: https://lore.kernel.org/r/20250612021417.44929-1-feng.tang@linux.alibaba.com

Merge tag 'dma-mapping-6.16-2025-05-26' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux

2025-05-28T03:09:06Z

Pull dma-mapping updates from Marek Szyprowski: "New two step DMA mapping API, which is is a first step to a long path to provide alternatives to scatterlist and to remove hacks, abuses and design mistakes related to scatterlists. This new approach optimizes some calls to DMA-IOMMU layer and cache maintenance by batching them, reduces memory usage as it is no need to store mapped DMA addresses to unmap them, and reduces some function call overhead. It is a combination effort of many people, lead and developed by Christoph Hellwig and Leon Romanovsky" * tag 'dma-mapping-6.16-2025-05-26' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux: docs: core-api: document the IOVA-based API dma-mapping: add a dma_need_unmap helper dma-mapping: Implement link/unlink ranges API iommu/dma: Factor out a iommu_dma_map_swiotlb helper dma-mapping: Provide an interface to allow allocate IOVA iommu: add kernel-doc for iommu_unmap_fast iommu: generalize the batched sync after map interface dma-mapping: move the PCI P2PDMA mapping helpers to pci-p2pdma.h PCI/P2PDMA: Refactor the p2pdma mapping helpers

dma-mapping: add a dma_need_unmap helper

2025-05-06T06:36:53Z

Add helper that allows a driver to skip calling dma_unmap_* if the DMA layer can guarantee that they are no-nops. Signed-off-by: Christoph Hellwig Tested-by: Jens Axboe Reviewed-by: Luis Chamberlain Signed-off-by: Leon Romanovsky Signed-off-by: Marek Szyprowski

dma-mapping: move the PCI P2PDMA mapping helpers to pci-p2pdma.h

2025-05-06T06:36:53Z

To support the upcoming non-scatterlist mapping helpers, we need to go back to have them called outside of the DMA API. Thus move them out of dma-map-ops.h, which is only for DMA API implementations to pci-p2pdma.h, which is for driver use. Note that the core helper is still not exported as the mapping is expected to be done only by very highlevel subsystem code at least for now. Signed-off-by: Christoph Hellwig Reviewed-by: Logan Gunthorpe Acked-by: Bjorn Helgaas Tested-by: Jens Axboe Reviewed-by: Luis Chamberlain Reviewed-by: Lu Baolu Signed-off-by: Leon Romanovsky Signed-off-by: Marek Szyprowski

PCI/P2PDMA: Refactor the p2pdma mapping helpers

2025-05-06T06:36:53Z

The current scheme with a single helper to determine the P2P status and map a scatterlist segment force users to always use the map_sg helper to DMA map, which we're trying to get away from because they are very cache inefficient. Refactor the code so that there is a single helper that checks the P2P state for a page, including the result that it is not a P2P page to simplify the callers, and a second one to perform the address translation for a bus mapped P2P transfer that does not depend on the scatterlist structure. Signed-off-by: Christoph Hellwig Reviewed-by: Logan Gunthorpe Acked-by: Bjorn Helgaas Tested-by: Jens Axboe Reviewed-by: Luis Chamberlain Reviewed-by: Lu Baolu Signed-off-by: Leon Romanovsky Signed-off-by: Marek Szyprowski

dma-coherent: Warn if OF reserved memory is beyond current coherent DMA mask

2025-04-22T15:44:09Z

When a reserved memory region described in the device tree is attached to a device, it is expected that the device's limitations are correctly included in that description. However, if the device driver failed to implement DMA address masking or addressing beyond the default 32 bits (on arm64), then bad things could happen because the DMA address was truncated, such as playing back audio with no actual audio coming out, or DMA overwriting random blocks of kernel memory. Check against the coherent DMA mask when the memory regions are attached to the device. Give a warning when the memory region can not be covered by the mask. A warning instead of a hard error was chosen, because it is possible that existing drivers could be working fine even if they forgot to extend the coherent DMA mask. Signed-off-by: Chen-Yu Tsai Signed-off-by: Marek Szyprowski Link: https://lore.kernel.org/r/20250421083930.374173-1-wenst@chromium.org

dma-mapping: Fix warning reported for missing prototype

2025-04-22T13:06:33Z

lkp reported a warning about missing prototype for a recent patch. The kernel-doc style comments are out of sync, move them to the right function. Cc: Marek Szyprowski Cc: Christoph Hellwig Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202504190615.g9fANxHw-lkp@intel.com/ Signed-off-by: Balbir Singh [mszyprow: reformatted subject] Signed-off-by: Marek Szyprowski Link: https://lore.kernel.org/r/20250422114034.3535515-1-balbirs@nvidia.com

dma/mapping.c: dev_dbg support for dma_addressing_limited

2025-04-14T14:10:50Z

In the debug and resolution of an issue involving forced use of bounce buffers, 7170130e4c72 ("x86/mm/init: Handle the special case of device private pages in add_pages(), to not increase max_pfn and trigger dma_addressing_limited() bounce buffers"). It would have been easier to debug the issue if dma_addressing_limited() had debug information about the device not being able to address all of memory and thus forcing all accesses through a bounce buffer. Please see[2] Implement dev_dbg to debug the potential use of bounce buffers when we hit the condition. When swiotlb is used, dma_addressing_limited() is used to determine the size of maximum dma buffer size in dma_direct_max_mapping_size(). The debug prints could be triggered in that check as well (when enabled). Link: https://lore.kernel.org/lkml/20250401000752.249348-1-balbirs@nvidia.com/ [1] Link: https://lore.kernel.org/lkml/20250310112206.4168-1-spasswolf@web.de/ [2] Cc: Marek Szyprowski Cc: Robin Murphy Cc: "Christian König" Cc: Ingo Molnar Cc: Kees Cook Cc: Bjorn Helgaas Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Alex Deucher Cc: Bert Karwatzki Cc: Christoph Hellwig Signed-off-by: Balbir Singh Reviewed-by: Christoph Hellwig Signed-off-by: Marek Szyprowski Link: https://lore.kernel.org/r/20250414113752.3298276-1-balbirs@nvidia.com

dma/contiguous: avoid warning about unused size_bytes

2025-04-09T15:28:53Z

When building with W=1, this variable is unused for configs with CONFIG_CMA_SIZE_SEL_PERCENTAGE=y: kernel/dma/contiguous.c:67:26: error: 'size_bytes' defined but not used [-Werror=unused-const-variable=] Change this to a macro to avoid the warning. Fixes: c64be2bb1c6e ("drivers: add Contiguous Memory Allocator") Signed-off-by: Arnd Bergmann Signed-off-by: Marek Szyprowski Link: https://lore.kernel.org/r/20250409151557.3890443-1-arnd@kernel.org

dma-mapping: fix missing clear bdr in check_ram_in_range_map()

2025-03-12T12:41:44Z

As discussed in [1], if 'bdr' is set once, it would never get cleared, hence 0 is always returned. Refactor the range check hunk into a new helper dma_find_range(), which allows 'bdr' to be cleared in each iteration. Link: https://lore.kernel.org/all/64931fac-085b-4ff3-9314-84bac2fa9bdb@quicinc.com/ # [1] Fixes: a409d9600959 ("dma-mapping: fix dma_addressing_limited() if dma_range_map can't cover all system RAM") Suggested-by: Christoph Hellwig Signed-off-by: Baochen Qiang Link: https://lore.kernel.org/r/20250307030350.69144-1-quic_bqiang@quicinc.com Signed-off-by: Marek Szyprowski