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iommufd: Clarify IOAS_MAP_FILE dma-buf support

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IOMMU_IOAS_MAP_FILE is documented as mapping a memfd, but the
implementation first tries to resolve the fd as a dma-buf and has a
special path for supported dma-buf exporters. In particular, VFIO PCI
dma-bufs exported through VFIO_DEVICE_FEATURE_DMA_BUF can be mapped when
they describe a single DMA range.

Update the UAPI comment so userspace understands that certain kinds of
dma-buf are supported in addition to memfd.

Fixes: 44ebaa1744 ("iommufd: Accept a DMABUF through IOMMU_IOAS_MAP_FILE")
Link: https://patch.msgid.link/r/20260610-tmp-v1-1-b8ccbf557391@fb.com
Signed-off-by: Alex Mastro <amastro@fb.com>
Assisted-by: Codex:gpt-5.5-high
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
This commit is contained in:
Alex Mastro 2026-06-10 13:44:41 -07:00 committed by Jason Gunthorpe
parent f2d70dbd3d
commit 298ab7e6f1
1 changed files with 8 additions and 4 deletions
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12
include/uapi/linux/iommufd.h
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@ -224,13 +224,17 @@ struct iommu_ioas_map {
* @size: sizeof(struct iommu_ioas_map_file)
* @flags: same as for iommu_ioas_map
* @ioas_id: same as for iommu_ioas_map
* @fd: the memfd to map
* @start: byte offset from start of file to map from
* @fd: the memfd or supported dma-buf file to map
* @start: byte offset from start of the file to map from
* @length: same as for iommu_ioas_map
* @iova: same as for iommu_ioas_map
*
* Set an IOVA mapping from a memfd file. All other arguments and semantics
* match those of IOMMU_IOAS_MAP.
* Set an IOVA mapping from a memfd file. On kernels with dma-buf support,
* supported dma-buf files may also be accepted. This is not a generic
* dma-buf import path; currently supported dma-bufs include single-range
* VFIO PCI dma-bufs exported through VFIO_DEVICE_FEATURE_DMA_BUF, and
* other dma-bufs may be rejected. All other arguments and semantics match
* those of IOMMU_IOAS_MAP.
*/
struct iommu_ioas_map_file {
__u32 size;