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

[fangyu . yu]

>> From: Fangyu Yu <fangyu.yu@xxxxxxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxxxx/
>> 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@xxxxxxxxxxxxxxxxx/
>> 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@xxxxxxxxxxxxxxxxx/
>>
>> [1] https://lore.kernel.org/linux-iommu/1-v2-563ee63886f0+1209-iommupt_armv8_jgg@xxxxxxxxxx/
>> [2] https://lore.kernel.org/linux-iommu/20260818092444.42755-1-andrew.jones@xxxxxxxxxxxxxxxx/
>>
>> 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.
>

Hi Shuai,

Thanks for catching that. You’re right — I missed patch 10/10, and it
was indeed omitted from the series. 
I’ll resend it.

Thanks,
Fangyu

>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(-)
>>