[PATCH v7 00/28] iommufd: Add vIOMMU infrastructure (Part-4 HW QUEUE)

Nicolin Chen
2025-06-26T19:40:13Z

The vIOMMU object is designed to represent a slice of an IOMMU HW for its
virtualization features shared with or passed to user space (a VM mostly)
in a way of HW acceleration. This extended the HWPT-based design for more
advanced virtualization feature.

HW QUEUE introduced by this series as a part of the vIOMMU infrastructure
represents a HW accelerated queue/buffer for VM to use exclusively, e.g.
- NVIDIA's Virtual Command Queue
- AMD vIOMMU's Command Buffer, Event Log Buffer, and PPR Log Buffer
each of which allows its IOMMU HW to directly access a queue memory owned
by a guest VM and allows a guest OS to control the HW queue direclty, to
avoid VM Exit overheads to improve the performance.

Introduce IOMMUFD_OBJ_HW_QUEUE and its pairing IOMMUFD_CMD_HW_QUEUE_ALLOC
allowing VMM to forward the IOMMU-specific queue info, such as queue base
address, size, and etc.

Meanwhile, a guest-owned queue needs the guest kernel to control the queue
by reading/writing its consumer and producer indexes, via MMIO acceses to
the hardware MMIO registers. Introduce an mmap infrastructure for iommufd
to support passing through a piece of MMIO region from the host physical
address space to the guest physical address space. The mmap info (offset/
length) used by an mmap syscall must be pre-allocated and returned to the
user space via an output driver-data during an IOMMUFD_CMD_HW_QUEUE_ALLOC
call. Thus, it requires a driver-specific user data support in the vIOMMU
allocation flow.

As a real-world use case, this series implements a HW QUEUE support in the
tegra241-cmdqv driver for VCMDQs on NVIDIA Grace CPU. In another word, it
is also the Tegra CMDQV series Part-2 (user-space support), reworked from
Previous RFCv1:
https://lore.kernel.org/all/cover.1712978212.git.nicolinc@nvidia.com/
This enables the HW accelerated feature for NVIDIA Grace CPU. Compared to
the standard SMMUv3 operating in the nested translation mode trapping CMDQ
for TLBI and ATC_INV commands, this gives a huge performance improvement:
70% to 90% reductions of invalidation time were measured by various DMA
unmap tests running in a guest OS.

// Unmap latencies from "dma_map_benchmark -g @granule -t @threads",
// by toggling "/sys/kernel/debug/iommu/tegra241_cmdqv/bypass_vcmdq"
@granule | @threads | bypass_vcmdq=1 | bypass_vcmdq=0
4KB 1 35.7 us 5.3 us
16KB 1 41.8 us 6.8 us
64KB 1 68.9 us 9.9 us
128KB 1 109.0 us 12.6 us
256KB 1 187.1 us 18.0 us
4KB 2 96.9 us 6.8 us
16KB 2 97.8 us 7.5 us
64KB 2 151.5 us 10.7 us
128KB 2 257.8 us 12.7 us
256KB 2 443.0 us 17.9 us

This is on Github:
https://github.com/nicolinc/iommufd/commits/iommufd_hw_queue-v7

Paring QEMU branch for testing:
https://github.com/nicolinc/qemu/commits/wip/for_iommufd_hw_queue-v7

Changelog
v7
* Rebased on Jason's for-next tree (iommufd_hw_queue-prep series)
* Add Reviewed-by from Baolu, Jason, Pranjal
* Update kdocs and notes
* [iommu] Replace "u32" with "enum iommu_hw_info_type"
* [iommufd] Rename vdev->id to vdev->virt_id
* [iommufd] Replace macros with inline helpers
* [iommufd] Report unmapped_bytes in error path
* [iommufd] Add iommufd_access_is_internal helper
* [iommufd] Do not drop ops->unmap check for mdevs
* [iommufd] Store physical addresses in immap structure
* [iommufd] Reorder access and hw_queue object allocations
* [iommufd] Scan for an internal access before any unmap call
* [iommufd] Drop unused ictx pointer in struct iommufd_hw_queue
* [iommufd] Use kcalloc to avoid failure due to memory fragmentation
* [tegra] Use "else"
* [tegra] Lock destroy() using lvcmdq_mutex
v6
https://lore.kernel.org/all/cover.1749884998.git.nicolinc@nvidia.com/
* Rebase on iommufd_hw_queue-prep-v2
* Add Reviewed-by from Kevin and Jason
* [iommufd] Update kdocs and notes
* [iommufd] Drop redundant pages[i] check
* [iommufd] Allow nesting_parent_iova to be 0
* [iommufd] Add iommufd_hw_queue_alloc_phys()
* [iommufd] Revise iommufd_viommu_alloc/destroy_mmap APIs
* [iommufd] Move destroy ops to vdevice/hw_queue structures
* [iommufd] Add union in hw_info struct to share out_data_type field
* [iommufd] Replace iopt_pin/unpin_pages() with internal access APIs
* [iommufd] Replace vdevice_alloc with vdevice_size and vdevice_init
* [iommufd] Replace hw_queue_alloc with get_hw_queue_size/hw_queue_init
* [iommufd] Replace IOMMUFD_VIOMMU_FLAG_HW_QUEUE_READS_PA with init_phys
* [smmu] Drop arm_smmu_domain_ipa_to_pa
* [smmu] Update arm_smmu_impl_ops changes for vsmmu_init
* [tegra] Add a vdev_to_vsid macro
* [tegra] Add lvcmdq_mutex to protect multi queues
* [tegra] Drop duplicated kcalloc for vintf->lvcmdqs (memory leak)
v5
https://lore.kernel.org/all/cover.1747537752.git.nicolinc@nvidia.com/
* Rebase on v6.15-rc6
* Add Reviewed-by from Jason and Kevin
* Correct typos in kdoc and update commit logs
* [iommufd] Add a cosmetic fix
* [iommufd] Drop unused num_pfns
* [iommufd] Drop unnecessary check
* [iommufd] Reorder patch sequence
* [iommufd] Use io_remap_pfn_range()
* [iommufd] Use success oriented flow
* [iommufd] Fix max_npages calculation
* [iommufd] Add more selftest coverage
* [iommufd] Drop redundant static_assert
* [iommufd] Fix mmap pfn range validation
* [iommufd] Reject unmap on pinned iovas
* [iommufd] Drop redundant vm_flags_set()
* [iommufd] Drop iommufd_struct_destroy()
* [iommufd] Drop redundant queue iova test
* [iommufd] Use "mmio_addr" and "mmio_pfn"
* [iommufd] Rename to "nesting_parent_iova"
* [iommufd] Make iopt_pin_pages call option
* [iommufd] Add ictx comparison in depend()
* [iommufd] Add iommufd_object_alloc_ucmd()
* [iommufd] Move kcalloc() after validations
* [iommufd] Replace ictx setting with WARN_ON
* [iommufd] Make hw_info's type bidirectional
* [smmu] Add supported_vsmmu_type in impl_ops
* [smmu] Drop impl report in smmu vendor struct
* [tegra] Add IOMMU_HW_INFO_TYPE_TEGRA241_CMDQV
* [tegra] Replace "number of VINTFs" with a note
* [tegra] Drop the redundant lvcmdq pointer setting
* [tegra] Flag IOMMUFD_VIOMMU_FLAG_HW_QUEUE_READS_PA
* [tegra] Use "vintf_alloc_vsid" for vdevice_alloc op
v4
https://lore.kernel.org/all/cover.1746757630.git.nicolinc@nvidia.com/
* Rebase on v6.15-rc5
* Add Reviewed-by from Vasant
* Rename "vQUEUE" to "HW QUEUE"
* Use "offset" and "length" for all mmap-related variables
* [iommufd] Use u64 for guest PA
* [iommufd] Fix typo in uAPI doc
* [iommufd] Rename immap_id to offset
* [iommufd] Drop the partial-size mmap support
* [iommufd] Do not replace WARN_ON with WARN_ON_ONCE
* [iommufd] Use "u64 base_addr" for queue base address
* [iommufd] Use u64 base_pfn/num_pfns for immap structure
* [iommufd] Correct the size passed in to mtree_alloc_range()
* [iommufd] Add IOMMUFD_VIOMMU_FLAG_HW_QUEUE_READS_PA to viommu_ops
v3
https://lore.kernel.org/all/cover.1746139811.git.nicolinc@nvidia.com/
* Add Reviewed-by from Baolu, Pranjal, and Alok
* Revise kdocs, uAPI docs, and commit logs
* Rename "vCMDQ" back to "vQUEUE" for AMD cases
* [tegra] Add tegra241_vcmdq_hw_flush_timeout()
* [tegra] Rename vsmmu_alloc to alloc_vintf_user
* [tegra] Use writel for SID replacement registers
* [tegra] Move mmap removal call to vsmmu_destroy op
* [tegra] Fix revert in tegra241_vintf_alloc_lvcmdq_user()
* [iommufd] Replace "& ~PAGE_MASK" with PAGE_ALIGNED()
* [iommufd] Add an object-type "owner" to immap structure
* [iommufd] Drop the ictx input in the new for-driver APIs
* [iommufd] Add iommufd_vma_ops to keep track of mmap lifecycle
* [iommufd] Add viommu-based iommufd_viommu_alloc/destroy_mmap helpers
* [iommufd] Rename iommufd_ctx_alloc/free_mmap to
_iommufd_alloc/destroy_mmap
v2
https://lore.kernel.org/all/cover.1745646960.git.nicolinc@nvidia.com/
* Add Reviewed-by from Jason
* [smmu] Fix vsmmu initial value
* [smmu] Support impl for hw_info
* [tegra] Rename "slot" to "vsid"
* [tegra] Update kdocs and commit logs
* [tegra] Map/unmap LVCMDQ dynamically
* [tegra] Refcount the previous LVCMDQ
* [tegra] Return -EEXIST if LVCMDQ exists
* [tegra] Simplify VINTF cleanup routine
* [tegra] Use vmid and s2_domain in vsmmu
* [tegra] Rename "mmap_pgoff" to "immap_id"
* [tegra] Add more addr and length validation
* [iommufd] Add more narrative to mmap's kdoc
* [iommufd] Add iommufd_struct_depend/undepend()
* [iommufd] Rename vcmdq_free op to vcmdq_destroy
* [iommufd] Fix bug in iommu_copy_struct_to_user()
* [iommufd] Drop is_io from iommufd_ctx_alloc_mmap()
* [iommufd] Test the queue memory for its contiguity
* [iommufd] Return -ENXIO if address or length fails
* [iommufd] Do not change @min_last in mock_viommu_alloc()
* [iommufd] Generalize TEGRA241_VCMDQ data in core structure
* [iommufd] Add selftest coverage for IOMMUFD_CMD_VCMDQ_ALLOC
* [iommufd] Add iopt_pin_pages() to prevent queue memory from unmapping
v1
https://lore.kernel.org/all/cover.1744353300.git.nicolinc@nvidia.com/

Thanks
Nicolin

Nicolin Chen (28):
iommufd: Report unmapped bytes in the error path of
iopt_unmap_iova_range
iommufd/viommu: Explicitly define vdev->virt_id
iommu: Use enum iommu_hw_info_type for type in hw_info op
iommu: Add iommu_copy_struct_to_user helper
iommu: Pass in a driver-level user data structure to viommu_init op
iommufd/viommu: Allow driver-specific user data for a vIOMMU object
iommufd/selftest: Support user_data in mock_viommu_alloc
iommufd/selftest: Add coverage for viommu data
iommufd/access: Add internal APIs for HW queue to use
iommufd/access: Bypass access->ops->unmap for internal use
iommufd/viommu: Add driver-defined vDEVICE support
iommufd/viommu: Introduce IOMMUFD_OBJ_HW_QUEUE and its related struct
iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC ioctl
iommufd/driver: Add iommufd_hw_queue_depend/undepend() helpers
iommufd/selftest: Add coverage for IOMMUFD_CMD_HW_QUEUE_ALLOC
iommufd: Add mmap interface
iommufd/selftest: Add coverage for the new mmap interface
Documentation: userspace-api: iommufd: Update HW QUEUE
iommu: Allow an input type in hw_info op
iommufd: Allow an input data_type via iommu_hw_info
iommufd/selftest: Update hw_info coverage for an input data_type
iommu/arm-smmu-v3-iommufd: Add vsmmu_size/type and vsmmu_init impl ops
iommu/arm-smmu-v3-iommufd: Add hw_info to impl_ops
iommu/tegra241-cmdqv: Use request_threaded_irq
iommu/tegra241-cmdqv: Simplify deinit flow in
tegra241_cmdqv_remove_vintf()
iommu/tegra241-cmdqv: Do not statically map LVCMDQs
iommu/tegra241-cmdqv: Add user-space use support
iommu/tegra241-cmdqv: Add IOMMU_VEVENTQ_TYPE_TEGRA241_CMDQV support

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 22 +-
drivers/iommu/iommufd/iommufd_private.h | 50 +-
drivers/iommu/iommufd/iommufd_test.h | 20 +
include/linux/iommu.h | 50 +-
include/linux/iommufd.h | 160 ++++++
include/uapi/linux/iommufd.h | 145 +++++-
tools/testing/selftests/iommu/iommufd_utils.h | 89 +++-
.../arm/arm-smmu-v3/arm-smmu-v3-iommufd.c | 28 +-
.../iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 484 +++++++++++++++++-
drivers/iommu/intel/iommu.c | 7 +-
drivers/iommu/iommufd/device.c | 90 +++-
drivers/iommu/iommufd/driver.c | 81 ++-
drivers/iommu/iommufd/io_pagetable.c | 17 +-
drivers/iommu/iommufd/main.c | 69 +++
drivers/iommu/iommufd/selftest.c | 153 +++++-
drivers/iommu/iommufd/viommu.c | 208 +++++++-
tools/testing/selftests/iommu/iommufd.c | 143 +++++-
.../selftests/iommu/iommufd_fail_nth.c | 15 +-
Documentation/userspace-api/iommufd.rst | 12 +
19 files changed, 1736 insertions(+), 107 deletions(-)

--
2.43.0