Re: [RFC PATCH v4 00/10] iommu/riscv: Add hardware dirty tracking for second-stage domains

[Gong Shuai <gsh517025@gmail.com>]

On 9/15/2026 11:28 AM, fangyu.yu@linux.alibaba.com wrote:
> From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
> 
> 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 v4 (Jason's suggestions):
>      - Rebased the series on top of [1] and [2].
>      - Drop the RISC-V-specific pt_num_items_lg2() top-level special case.
>      - Validate page-table address widths by translation stage: accept only
>        Sv39/Sv48/Sv57 widths for first-stage tables and only Sv39x4/Sv48x4/
>        Sv57x4 widths for second-stage tables.
>      - Replace the aliased first-stage/second-stage MODE union with
>        independent FSC/IOSATP and IOHGATP MODE fields.
>      - Add pt_dirty_supported() to restrict RISC-V generic_pt dirty tracking
>        to second-stage tables.
>      - Link to v3:
>        https://lore.kernel.org/linux-riscv/20260821132749.82070-1-fangyu.yu@linux.alibaba.com/
> 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/20260507113706.11400-1-fangyu.yu@linux.alibaba.com/
> 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/20260428131359.34872-1-fangyu.yu@linux.alibaba.com/
> 
> [1] https://lore.kernel.org/linux-iommu/1-v2-563ee63886f0+1209-iommupt_armv8_jgg@nvidia.com/
> [2] https://lore.kernel.org/linux-iommu/20260818092444.42755-1-andrew.jones@oss.qualcomm.com/
> 
> 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 domainsgon
>    iommu/riscv: Add dirty tracking support for second-stage domains
>    iommu/riscv: Add IOTINVAL.GVMA after updating DDT/PDT entries

Hi Fangyu,

This patch (10/10) is missing from this series.
It was also missing in RFC v3.

Thanks,
Shuai

> 
> 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         | 158 +++++++++++--
>   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             |  11 +
>   7 files changed, 336 insertions(+), 72 deletions(-)
>