[PATCH v4 0/8] drm/amdkfd: Add batch userptr allocation support

[Honglei Huang <honglei1.huang@amd.com>]

From: Honglei Huang <honghuan@amd.com>

Hi all,

This is v4 of the patch series to support allocating multiple non-contiguous
CPU virtual address ranges that map to a single contiguous GPU virtual address.

v4:
1. Fixed hmm_range.notifier_seq limitation: add per-range 'valid' flag
   - Use explicit 'valid' flag instead of notifier seq in user_range_info
     to track whether each range's pages are valid or have been invalidated

2. Fixed mmap_read_lock usage: hold mmap_read_lock across entire batch
   page fault operation instead of per-range locking
   - Renamed get_user_pages_batch() to get_user_pages_batch_locked()
   - Caller now holds mmap_read_lock for entire batch operation

3. Improved error handling: Better cleanup paths and error messages

v3:
1. No new ioctl: Reuses existing AMDKFD_IOC_ALLOC_MEMORY_OF_GPU
   - Adds only one flag: KFD_IOC_ALLOC_MEM_FLAGS_USERPTR_BATCH
   - When flag is set, mmap_offset field points to range array
   - Minimal API surface change

2. Improved MMU notifier handling:
   - Single mmu_interval_notifier covering the VA span [va_min, va_max]
   - Interval tree for efficient lookup of affected ranges during invalidation
   - Avoids per-range notifier overhead mentioned in v2 review

3. Better code organization: Split into 8 focused patches for easier review

v2:
   - Each CPU VA range gets its own mmu_interval_notifier for invalidation
   - All ranges validated together and mapped to contiguous GPU VA
   - Single kgd_mem object with array of user_range_info structures
   - Unified eviction/restore path for all ranges in a batch

Current Implementation Approach
===============================

This series implements a practical solution within existing kernel constraints:

1. Single MMU notifier for VA span: Register one notifier covering the
   entire range from lowest to highest address in the batch

2. Interval tree filtering: Use interval tree to efficiently identify
   which specific ranges are affected during invalidation callbacks,
   avoiding unnecessary processing for unrelated address changes

3. Unified eviction/restore: All ranges in a batch share eviction and
   restore paths, maintaining consistency with existing userptr handling

Patch Series Overview
=====================

Patch 1/8: Add userptr batch allocation UAPI structures
    - KFD_IOC_ALLOC_MEM_FLAGS_USERPTR_BATCH flag
    - kfd_ioctl_userptr_range and kfd_ioctl_userptr_ranges_data structures

Patch 2/8: Add user_range_info infrastructure to kgd_mem
    - user_range_info structure for per-range tracking
    - Fields for batch allocation in kgd_mem

Patch 3/8: Implement interval tree for userptr ranges
    - Interval tree for efficient range lookup during invalidation
    - mark_invalid_ranges() function

Patch 4/8: Add batch MMU notifier support
    - Single notifier for entire VA span
    - Invalidation callback using interval tree filtering

Patch 5/8: Implement batch userptr page management
    - get_user_pages_batch_locked() and set_user_pages_batch()
    - Per-range page array management

Patch 6/8: Add batch allocation function and export API
    - init_user_pages_batch() main initialization
    - amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu_batch() entry point

Patch 7/8: Unify userptr cleanup and update paths
    - Shared eviction/restore handling for batch allocations
    - Integration with existing userptr validation flows

Patch 8/8: Wire up batch allocation in ioctl handler
    - Input validation and range array parsing
    - Integration with existing alloc_memory_of_gpu path

Testing
=======

- Multiple scattered malloc() allocations (2-4000+ ranges)
- Various allocation sizes (4KB to 1G+ per range)
- Memory pressure scenarios and eviction/restore cycles
- OpenCL CTS and HIP catch tests in KVM guest environment
- AI workloads: Stable Diffusion, ComfyUI in virtualized environments
- Small LLM inference (3B-7B models)
- Benchmark score: 160,000 - 190,000 (80%-95% of bare metal)
- Performance improvement: 2x-2.4x faster than userspace approach

Thank you for your review and feedback.

Best regards,
Honglei Huang

Honglei Huang (8):
  drm/amdkfd: Add userptr batch allocation UAPI structures
  drm/amdkfd: Add user_range_info infrastructure to kgd_mem
  drm/amdkfd: Implement interval tree for userptr ranges
  drm/amdkfd: Add batch MMU notifier support
  drm/amdkfd: Implement batch userptr page management
  drm/amdkfd: Add batch allocation function and export API
  drm/amdkfd: Unify userptr cleanup and update paths
  drm/amdkfd: Wire up batch allocation in ioctl handler

 drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h    |  23 +
 .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c  | 559 +++++++++++++++++-
 drivers/gpu/drm/amd/amdkfd/kfd_chardev.c      | 128 +++-
 include/uapi/linux/kfd_ioctl.h                |  31 +-
 4 files changed, 717 insertions(+), 24 deletions(-)

-- 
2.34.1