[RFC PATCH v3 00/10] iommu/riscv: Add hardware dirty tracking for second-stage domains

From: Fangyu Yu <[email protected]>

The RISC-V IOMMU architecture defines an AMO_HWAD capability (Hardware
Access/Dirty update) that allows the IOMMU to atomically set the A/D bits
in second-stage PTEs on DMA access.  When DC.tc.GADE is asserted, the IOMMU
autonomously sets D on the first write to a page mapped by an iohgatp
domain.  This series wires that capability up to the iommufd dirty-tracking
interface (IOMMU_HWPT_SET_DIRTY_TRACKING / IOMMU_HWPT_GET_DIRTY_BITMAP) and
reports IOMMU_CAP_DIRTY_TRACKING.

Design notes
------------

* The feature is scoped to second-stage (iohgatp) domains only; these are
  the domains created for KVM / VFIO device pass-through when userspace
  allocates an HWPT with IOMMU_HWPT_ALLOC_NEST_PARENT or
  IOMMU_HWPT_ALLOC_DIRTY_TRACKING.  First-stage (iosatp) domains are not
  touched by this series.

* The page-table side plugs into the existing generic_pt dirty hook
  framework (amdv1 / vtdss style).  RISC-V adds the three required PTE
  ops – is_write_dirty / make_write_clean / make_write_dirty.

Testing
-------

* Test on QEMU RISC-V, a nvme and an e1000e device was passed through
  to an L2 guest via vfio-pci + iommufd.

* generic_pt KUnit: the existing test_dirty case now runs and passes for
  the RISC-V 64-bit format.

Follow-up work
--------------
* Build a dedicated end-to-end test case that drives the full flow
  (HWPT_ALLOC with DIRTY_TRACKING -> attach -> IOAS_MAP -> generate real
  DMA -> SET_DIRTY_TRACKING -> GET_DIRTY_BITMAP -> verify bitmap against
  expected IOVA footprint) so that the behaviour can be regression-tested
  beyond the KUnit PTE-level coverage.

* If possible, rebase and retest on top of the updated "iommu irqbypass"
  patchset.

---
Changes in v3 (Andrew Jones's suggestions):
    - Rebased the series on top of Andrew Jones' generic_pt RISC-V supported
      feature mask fix, which adds PT_FEAT_RISCV_SVPBMT to the supported feature
      set.
    - Added PT_FEAT_RISCV_S2 to the RISC-V generic_pt supported feature mask and
      KUnit feature matrix.
    - Kept PT_FEAT_SIGN_EXTEND only for first-stage RISC-V KUnit configs; second
      stage configs now use PT_FEAT_RISCV_S2 without sign-extension semantics.
    - Split RISC-V IOMMU capability checks into first-stage FSC and second-stage
      IOHGATP helpers.
    - Updated second-stage paging domain setup to use GPA widths 41/50/59 and to
      avoid PT_FEAT_SIGN_EXTEND.
    - Link to v2:
      https://lore.kernel.org/linux-riscv/[email protected]/
Changes in v2 (Jason's suggestions):
    - Introduced a single PT_FEAT_RISCV_S2: second-stage selection is driven
      purely by this feature bit.
    - Switched from dynamic DC.tc.GADE toggling to static pre-enable.
    - domain_alloc_paging_flags: follow the switch/case design from other
      drivers.
    - Drop IOMMU_CAP_DEFERRED_FLUSH in riscv_iommu_capable.
    - Remove the .hw_info-related patch.
    - Link to v1:
      https://lore.kernel.org/linux-riscv/[email protected]/

Fangyu Yu (6):
  iommupt: Add RISC-V Second-stage (iohgatp) page table support
  iommupt: Add RISC-V dirty tracking PTE ops
  iommu/riscv: Add domain_alloc_paging_flags for second-stage domain
  iommu/riscv: Pre-enable GADE for second-stage domains
  iommu/riscv: Add dirty tracking support for second-stage domains
  iommu/riscv: Add IOTINVAL.GVMA after updating DDT/PDT entries

Tomasz Jeznach (2):
  iommu/riscv: report iommu capabilities
  RISC-V: KVM: Enable KVM_VFIO interfaces on RISC-V arch

Zong Li (2):
  iommu/riscv: use data structure instead of individual values
  iommu/riscv: support GSCID and GVMA invalidation command

 arch/riscv/kvm/Kconfig                       |   2 +
 drivers/iommu/generic_pt/fmt/iommu_riscv64.c |   2 +-
 drivers/iommu/generic_pt/fmt/riscv.h         | 120 +++++++++-
 drivers/iommu/riscv/iommu-bits.h             |   7 +
 drivers/iommu/riscv/iommu.c                  | 224 +++++++++++++++----
 include/linux/generic_pt/common.h            |   4 +
 include/linux/generic_pt/iommu.h             |  17 +-
 7 files changed, 317 insertions(+), 59 deletions(-)

-- 
2.50.1


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