On Tue, 11 Nov 2025 06:52:01 -0800 Alex Mastro amastro@fb.com wrote:
Not all IOMMUs support the same virtual address width as the processor, for instance older Intel consumer platforms only support 39-bits of IOMMU address space. On such platforms, using the virtual address as the IOVA and mappings at the top of the address space both fail.
VFIO and IOMMUFD have facilities for retrieving valid IOVA ranges, VFIO_IOMMU_TYPE1_INFO_CAP_IOVA_RANGE and IOMMU_IOAS_IOVA_RANGES, respectively. These provide compatible arrays of ranges from which we can construct a simple allocator and record the maximum supported IOVA address.
Use this new allocator in place of reusing the virtual address, and incorporate the maximum supported IOVA into the limit testing. This latter change doesn't test quite the same absolute end-of-address space behavior but still seems to have some value. Testing for overflow is skipped when a reduced address space is supported as the desired errno is not generated.
This series is based on Alex Williamson's "Incorporate IOVA range info" [1] along with feedback from the discussion in David Matlack's "Skip vfio_dma_map_limit_test if mapping returns -EINVAL" [2].
Given David's plans to split IOMMU concerns from devices as described in [3], this series' home for `struct iova_allocator` and IOVA range helpers are likely to be short lived, since they reside in vfio_pci_device.c. I assume that the rework can move this functionality to a more appropriate location next to other IOMMU-focused code, once such a place exists.
[1] https://lore.kernel.org/all/20251108212954.26477-1-alex@shazbot.org/#t [2] https://lore.kernel.org/all/20251107222058.2009244-1-dmatlack@google.com/ [3] https://lore.kernel.org/all/aRIoKJk0uwLD-yGr@google.com/
To: Alex Williamson alex@shazbot.org To: David Matlack dmatlack@google.com To: Shuah Khan shuah@kernel.org To: Jason Gunthorpe jgg@ziepe.ca Cc: kvm@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Alex Mastro amastro@fb.com
Changes in v2:
- Fix various nits
- calloc() where appropriate
- Update overflow test to run regardless of iova range constraints
- Change iova_allocator_init() to return an allocated struct
- Unfold iova_allocator_alloc()
- Fix iova allocator initial state bug
- Update vfio_pci_driver_test to use iova allocator
- Link to v1: https://lore.kernel.org/r/20251110-iova-ranges-v1-0-4d441cf5bf6d@fb.com
Minor comments, but otherwise LGTM and passes testing on a Kaby Lake system with limited IOMMU address width. Thanks,
Alex