[PATCH 0/3] iommupt: Unmap and return the PFNs in one walk

[Fred Griffoul <griffoul@gmail.com>]

From: Fred Griffoul <fgriffo@amazon.co.uk>

When iommufd unmaps an area, it must unpin the user pages, but it keeps
no list of their PFNs. It reads each one back from the IOMMU domain
with iommu_iova_to_phys(), one CPU page at a time, then walks the page
table again in iommu_unmap(). With 4 KiB pages, a 1 GiB IOPTE costs
262144 lookups before the unmap starts.

This series lets the iommupt unmap walk report the physical range of
each IOPTE as it removes it, so iommufd unmaps and collects the PFNs
in one walk. The walk also steps over holes, where iommu_unmap() stops
at the first one.

Patch 1 adds iommu_unmap_sparse(), patch 2 uses it in
iopt_area_unpin_domain(), and patch 3 adds a selftest for the areas
that keep the per-page read-back.

An earlier series [1] proposed iova_to_phys_length() so that iommufd
can read the PFNs back one IOPTE at a time instead of one page at a
time. The unmap is still a second walk there. This series collects
the PFNs in the unmap walk itself.

The series applies to iommu/next. I wrote parts of the code and the
changelogs with Kiro, an AI coding assistant using Claude models, and
used it to run the tests. I reviewed and tested all of it.

[1] https://lore.kernel.org/linux-iommu/20260603151804.1963871-1-guanghuifeng@linux.alibaba.com/

Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>

Fred Griffoul (3):
  iommupt: Add iommu_unmap_sparse()
  iommufd: Use iommu_unmap_sparse() to unpin domain pages
  iommufd/selftest: Unmap areas that start inside a CPU page

 drivers/iommu/generic_pt/iommu_pt.h       |  61 ++++++++-
 drivers/iommu/generic_pt/kunit_iommu_pt.h | 144 ++++++++++++++++++++++
 drivers/iommu/iommu-debug-pagealloc.c     |  13 ++
 drivers/iommu/iommu-priv.h                |  24 ++++
 drivers/iommu/iommu.c                     |  76 ++++++++++++
 drivers/iommu/iommufd/pages.c             |  98 ++++++++++++++-
 include/linux/generic_pt/iommu.h          |  24 ++++
 include/linux/iommu.h                     |  22 ++++
 tools/testing/selftests/iommu/iommufd.c   |  30 +++++
 9 files changed, 486 insertions(+), 6 deletions(-)


base-commit: 2cf4be57b301ed2d7af82e70cff5dfd96894d8de
-- 
2.47.3