[PATCH 0/2] iommufd: Keep dmabuf MMIO attributes in domains added later

[Andrea Parri <parri.andrea@gmail.com>]

A VFIO PCI dmabuf mapped into an IOAS gets IOMMU_MMIO only in the domains
that exist when it is mapped. A domain attached afterwards, or an
IOMMU_IOAS_COPY of the area, reads the PFNs back from the existing
domain and maps the BAR as cacheable CPU memory. Patch 1 always takes
dmabuf PFNs from the recorded phys range instead.

Sashiko first reported this on patch 6 of David Woodhouse's RFC "KVM:
Allow alternative providers of guest_memfd backed by PFNMAP memory",
which picks the batch kind in pfn_reader_fill_dmabuf() from the
exporter's memory type. This fix does not depend on that series and
combines with it: with both, a domain added later gets the kind the
exporter reports.

The mock page table has no memory type bits, so the existing selftests
cannot see the difference. Patch 2 makes the mock record, per domain,
the pages mapped with IOMMU_MMIO, adds IOMMU_TEST_OP_MD_CHECK_MMIO, and
checks the domain filled later in two new tests, dmabuf_mmio_new_domain
and dmabuf_mmio_copy.

Tested on x86-64 under virtme-ng with CONFIG_IOMMUFD_TEST=y. Without
patch 1 both new tests fail on the second domain in all three mock
domain variants; in dmabuf_mmio_new_domain, a temporary print in
batch_to_domain() showed that domain mapped with IOMMU_READ |
IOMMU_WRITE | IOMMU_CACHE, where the first got IOMMU_READ | IOMMU_WRITE |
IOMMU_MMIO. With patch 1 the dmabuf tests pass.

Not tested on hardware that uses the memory type bits (ARM SMMUv3, AMD
with SME, RISC-V).

Andrea Parri (2):
  iommufd: Keep dmabuf PFNs MMIO when filling another domain
  iommufd/selftest: Check dmabuf MMIO mappings filled from another domain

 drivers/iommu/iommufd/iommufd_test.h          |  5 ++
 drivers/iommu/iommufd/pages.c                 | 13 ++-
 drivers/iommu/iommufd/selftest.c              | 90 +++++++++++++++++++
 tools/testing/selftests/iommu/iommufd.c       | 51 +++++++++++
 tools/testing/selftests/iommu/iommufd_utils.h | 13 +++
 5 files changed, 168 insertions(+), 4 deletions(-)

-- 
2.53.0