[PATCH v10 0/5] drm/gpusvm: split MM and device state across gpusvm/range/pages

[Honglei Huang <honghuan@amd.com>]

The intent of this series is to make drm_gpusvm more flexible and give
drivers more freedom over how they assemble the MM related and device
side operations. It implements the direction Matt suggested in [1]:
Mirror MR in gitlab: [4]

  - Move struct drm_gpusvm_pages out of struct drm_gpusvm_range.
  - Embed a struct drm_device in struct drm_gpusvm_pages and drive all
    DMA through it.
  - Drop struct drm_device from struct drm_gpusvm.
  - Have the driver's range structure embed one or more struct
    drm_gpusvm_pages in addition to struct drm_gpusvm_range.
  - Drop the range-based helpers (drm_gpusvm_range_pages_valid,
    drm_gpusvm_range_get_pages, drm_gpusvm_range_unmap_pages) and update
    drivers to use the drm_gpusvm_pages helpers instead.

In essence the series does only two abstractions, plus the xe
adaptation that follows from them:

  - range vs pages: split drm_gpusvm_range (MM / VA range state) from
    drm_gpusvm_pages (device physical related), so the two sides can
    have independent lifetimes and ownership.
  - drm_gpusvm vs drm_device: make drm_gpusvm pure MM level and push
    the device side down onto drm_gpusvm_pages, which is where DMA
    actually happens.
  - xe is updated to fit the modifications, no functional change
    intended.

V10:
  Fix two issues found by the AI review:
  - patch 1: fix a KCSAN data race in xe_svm_alloc_vram(): read
    range->base.flags.__flags with READ_ONCE() and assert on a local
    copy, pairing with the WRITE_ONCE() in
    drm_gpusvm_range_set_unmapped().
  - patch 3: remove the DMA unmap in xe_svm_fini(): since
    drm_gpusvm_range_remove() no longer unmaps synchronously, explicitly
    drm_gpusvm_unmap_pages() all remaining ranges before
    drm_gpusvm_fini().

V9:
  - patch 3: fix the build with CONFIG_DRM_XE_GPUSVM disabled: move
    pages out of the nested base struct in the stub xe_svm_range and
    route has_dma_mapping through range->pages. No functional change.

V8:
  - patch 4: add reviewed-by for Matt's review.

V7:
  - patch 1: split MM state flags: the AI review found a KCSAN / memory
    model cleanliness issue. Address it for consistency with
    drm_gpusvm_pages_flags, set the range flags with WRITE_ONCE() on
    __flags and read them with READ_ONCE().

V6:
  - The AI review flagged a potential DMA free issue: the DMA unmap
    step was moved into the range_free callback, but on the invalidate
    path a range can be removed from the MMU interval tree while its DMA
    mappings are still live, so a concurrent unmap event can miss it.
  - patch 3: have xe_svm_range embed one drm_gpusvm_pages: explicitly
    call drm_gpusvm_unmap_pages() before drm_gpusvm_range_remove() in the
    garbage collector, so a range is never off the tree while still DMA
    mapped, and document this caller contract in drm_gpusvm_range_remove()
    kernel-doc.
  - patch 4: move struct drm_gpusvm_pages out: document the
    unmap before remove contract in the garbage collector example and
    note that range_free()'s drm_gpusvm_free_pages() as a final fallback.
  - patch 1: split MM state flags: return -EACCES directly.
  - Fold in the pre existing IOVA/DMA unmap fixes the AI review found
    previously sent separately: the uninitialized dma_addr[0].dir on
    the get_pages() error path, the whole reservation IOVA free for
    mixed ranges, and the device mapping leak on the get_pages() error
    path. [6]

V5:
  - add reviewed-by in patches 1, 2, 3, 5 for Matt's review.

V4:
  - drm_gpusvm_init_pages(): memset() the pages to zero before recording
    the owning drm_device.
  - DOC: overview: recommend a zeroing allocator: kcalloc() for the
    N:1 pages array.
  - Rebased onto the latest drm-xe.
  - The AI review of this series flagged two preexisting issues in the
    IOVA unmap path that are not introduced by this series; they are
    fixed in a separate series [5].

V3:
  - Fix a kernel-doc/Sphinx warning from the kernel test robot: use
    ".. code-block:: c" for the drm_gpusvm_pages example in DOC: overview.
  - drm_gpusvm_range_set_unmapped(): use WRITE_ONCE() on the whole
    pages[i].flags.__flags word to pair with the lockless READ_ONCE()
    readers and avoid a data race.
  - xe_userptr_setup(): call drm_gpusvm_init_pages() before
    mmu_interval_notifier_insert() to avoid exposing uninitialized
    pages.drm to invalidation callbacks.
  - Fix per commit build of the set_unmapped() pages.

V2:
  - Followed in Matt's v0 review fixups [2]:
     - keep unmapped flag in pages structures.
     - add pages_count to drm_gpusvm_range_set_unmapped() to set the pages
       unmapped flag, so the framework can check unmapped status in
       drm_gpusvm_get_pages().
  - Add drm_gpusvm_init_pages to init the drm_device and sequence number.
  - Remove drm_device from drm_gpusvm_get_pages() parameters.
  - Reworked the DOC: overview and usage examples to describe the new
    model: struct drm_gpusvm_pages, the 1:1 / N:1 driver layouts, and
    examples that operate on a driver embedded pages object by the
    drm_gpusvm_pages helpers and etc.
  - remove WARN_ON_ONCE in __drm_gpusvm_unmap_pages.
  - Dropped RFC.

Follow-up (not in this series):

  - modify drm_gpusvm_get_pages() to support one time hmm range fault
    and multi drm device dma mapping.
  - Add no dma device support for drm_gpusvm_get_pages().

tests:
AMDGPU:
  based on amdgpu adaptation patch in [3], but still SVM:DRM = 1:1,
  1:n is on going needs many modifications and testings.

  Tested on gfx943 (MI300X) and gfx906 (MI60) with XNACK on/off:
  - KFD test: 95%+ passed.
  - ROCR test: all passed.
  - HIP catch test: gfx943 (MI300X): 99% passed.
                    gfx906 (MI60): 99% passed.
INTEL XE:
  CI tests passed in rev5 tests.[7]

links:
[1] https://lore.kernel.org/amd-gfx/acRgr7QwdULsn6G2@gsse-cloud1/#:~:text=I%20think%20roughly,drm_gpusvm_pages%0A%20%20helpers%20instead.
[2] https://gitlab.freedesktop.org/mbrost/xe-kernel-driver-svn-perf-6-15-2025/-/commit/623f6a50c037d9e44f6c9fbe6859a0ba7ad50177
[3] https://lore.kernel.org/amd-gfx/20260603065030.2554403-1-honglei1.huang@amd.com/
[4] https://gitlab.freedesktop.org/drm/xe/kernel/-/merge_requests/360
[5] https://lore.kernel.org/all/20260627033325.3795298-1-honglei1.huang@amd.com/
[6] https://lore.kernel.org/all/20260628061757.4093701-1-honglei1.huang@amd.com/
[7] https://patchwork.freedesktop.org/series/169384/#rev5

Honglei Huang (5):
  drm/gpusvm: split MM state flags out of drm_gpusvm_pages_flags
  drm/gpusvm: embed struct drm_device into drm_gpusvm_pages
  drm/xe: have xe_svm_range embed one drm_gpusvm_pages
  drm/gpusvm: move struct drm_gpusvm_pages out of struct
    drm_gpusvm_range
  drm/gpusvm: let the drm_gpusvm core context purely MM level

 drivers/gpu/drm/drm_gpusvm.c    | 243 +++++++++++++++++++-------------
 drivers/gpu/drm/xe/xe_pt.c      |   2 +-
 drivers/gpu/drm/xe/xe_svm.c     |  66 +++++++--
 drivers/gpu/drm/xe/xe_svm.h     |  14 +-
 drivers/gpu/drm/xe/xe_userptr.c |   5 +-
 include/drm/drm_gpusvm.h        |  67 ++++++---
 6 files changed, 255 insertions(+), 142 deletions(-)

-- 
2.34.1