drm/amdgpu: AMDGPU SVM support based on DRM (Phase 1: single GPU, XNACK on)

Hi Christian, Philip, Alex, Felix, and all,

These series introduce a new Shared Virtual Memory (SVM) implementation for
amdgpu that is built directly on top of the common DRM GPUSVM / drm_pagemap
core (drivers/gpu/drm/drm_gpusvm.c, drm_pagemap.c) rather than on the
existing KFD-private SVM code in amdkfd/kfd_svm.c.

The goal is to provide HMM-based unified memory through the same shared
infrastructure that the Xe driver already uses, so that amdgpu and xe
converge on one well-reviewed SVM/page-migration core instead of
maintaining a separate amdgpu-specific stack.

Phased plan
===========

This work is being upstreamed in phases to keep each submission reviewable:

  * Phase 1 (this series): single GPU, XNACK on (retry faults).

  * Phase 2 (in progress): single GPU, XNACK off (no-retry / eager mapping).
     - https://lore.kernel.org/amd-gfx/20260529054928.596825-1-h...
     - https://lore.kernel.org/amd-gfx/20260605075340.20199-1-Ju...

  * Phase 3 (in progress): multiple GPUs (XGMI mapping, P2P device-to-device migration).
     - https://lore.kernel.org/amd-gfx/20260603065620.2555316-1-...

Accordingly, this first submission targets the simplest useful configuration:

 * Single GPU with local VRAM migration: transparent RAM <-> VRAM page
   migration on one GPU via SDMA, with TTM-based eviction for overcommit.
 * XNACK on (retry faults): GPU page faults are retried after the driver
   lazily populates PTEs on demand. The XNACK-off/eager-mapping path is
   deferred to Phase 2.
 * Compute VMs only (amdgpu_vm_make_compute()), matching the KFD SVM
   use case.

Everything is gated behind a new, default-n Kconfig option
(CONFIG_DRM_AMDGPU_SVM) and is therefore opt-in and isolated from existing
users until the feature matures.

UAPI
====

A new render-node ioctl, DRM_IOCTL_AMDGPU_GEM_SVM, lets userspace describe SVM
attributes over a CPU virtual-address interval (patch 1):

  - operations: SET_ATTR / GET_ATTR / RESET_ATTR
  - access modes: INACCESSIBLE / IN_PLACE / ALLOW_MIGRATE
  - location hints: SYSMEM / UNDEFINED (preferred_loc, prefetch_loc)
  - per-range flags: HOST_ACCESS, COHERENT, EXT_COHERENT, HIVE_LOCAL,
    GPU_RO, GPU_EXEC, GPU_READ_MOSTLY, plus a granularity hint

Attributes are stored in a per-VM interval tree; the GPU page tables are
populated lazily on demand by retry faults, or eagerly on a prefetch request.

User Space Work
===============

  - ROCm UMD interface adaptation for the new drm SVM API is being
    developed in:
    https://github.com/ROCm/rocm-systems/pull/4364

Design Overview
===============

The implementation is split into clearly layered modules:

  amdgpu_svm.c            Core context (struct amdgpu_svm embeds
                          struct drm_gpusvm), kref lifecycle, PASID lookup,
                          drm_gpusvm_ops, the GEM_SVM ioctl entry point, and
                          the GC workqueue.
  amdgpu_svm_attr.c       The attribute interval tree: validation, gap/overlap
                          split-merge, SET/GET/RESET, and change-trigger
                          classification that decides whether an attribute
                          change needs PTE invalidation or a remap.
  amdgpu_svm_range.c      Per-range GPU mapping: PTE-flag computation per GC IP
                          version, DMA-segment coalescing, MMU-notifier
                          begin/end handling, PTE zapping, and the garbage
                          collector.
  amdgpu_svm_fault.c      The retry-fault entry point amdgpu_svm_handle_fault()
                          and the fault_map_range() pipeline.
  amdgpu_migrate.c        drm_pagemap / ZONE_DEVICE VRAM migration backend.
  amdgpu_svm_range_migrate.c  Per-range RAM<->VRAM migration helpers.

Fault path (XNACK on):
amdgpu_vm_handle_fault() routes a compute-VM retry fault to
amdgpu_svm_handle_fault() when the VM has an SVM context. After PASID lookup
and a checkpoint-timestamp filter that drops stale retry faults left over from
a recent unmap, it looks up (or synthesizes a default) attribute range and runs
fault_map_range(): garbage-collect -> VMA permission check -> find/insert range
-> short-circuit if recently validated or already valid -> drm_gpusvm get_pages
(HMM) -> program GPU PTEs under the notifier lock with a notifier-sequence
re-check.

Invalidation / GC:
MMU-notifier callbacks zap the affected PTEs (batched, single heavyweight TLB
flush) and, for unmap events, queue the range to a high-priority GC workqueue
that removes it via drm_gpusvm_range_remove() outside notifier context.

VRAM migration (patches 13-18):
A drm_pagemap is registered over the GPU's VRAM as a ZONE_DEVICE region at
device-init / reset-restore time. struct amdgpu_bo_svm (a new BO subtype)
backs migrated ranges, with SDMA-based copy_to_devmem / copy_to_ram callbacks
using a GART window. TTM eviction of SVM BOs synchronously migrates pages back
to system memory, which keeps VRAM overcommit working. The fault and prefetch
paths call amdgpu_svm_range_migrate_to_vram() before mapping when migration is
requested, with a single -EBUSY retry that evicts conflicting pages first.

Test Results
============

Tested on gfx943 (MI300X) and gfx906 (MI60) with XNACK on:
 - KFD test: 95%+ passed.
 - ROCR test: all passed.
 - HIP catch test: gfx943 (MI300X): 99% passed. gfx906 (MI60): 99% passed.

Changes from Old Version
========================

In this V8 version, we have consolidated all implementations for the
single-GPU XNACK-on mode. This approach follows Christian's suggestion to
make the code review process more straightforward.

Previously, the XNACK-on implementation was split into two parts:

 - Basic V7
   https://lore.kernel.org/amd-gfx/20260529054804.596214-1-h...
 - Migration V5
   https://lore.kernel.org/amd-gfx/20260605075340.20199-1-Ju...

Above two parts are no longer needed to be reviewed separately, please
focus on this series.

Thanks,
Ray/Honglei/Junhua

Honglei Huang (12):
  drm/amdgpu: add SVM ioctl UAPI definitions
  drm/amdgpu: add SVM core header and VM integration
  drm/amdgpu: add SVM attribute subsystem types
  drm/amdgpu: implement SVM attribute tree and helper functions
  drm/amdgpu: implement SVM attribute set/get/clear operations
  drm/amdgpu: add SVM range types and work queue interface
  drm/amdgpu: implement SVM range GPU mapping core
  drm/amdgpu: implement SVM range notifier and GC helpers
  drm/amdgpu: add SVM notifier invalidate callback and checkpoint
  drm/amdgpu: implement SVM initialization and lifecycle
  drm/amdgpu: add SVM ioctl entry and fault handler module
  drm/amdgpu: integrate SVM into build system and VM fault path

Junhua Shen (6):
  drm/amdgpu: add VRAM migration infrastructure for drm_pagemap
  drm/amdgpu: implement drm_pagemap SDMA migration callbacks
  drm/amdgpu: implement synchronous TTM eviction for SVM BOs
  drm/amdgpu: hook up ZONE_DEVICE registration in device init and reset
  drm/amdgpu: add SVM range migration helpers for drm_pagemap
  drm/amdgpu: integrate VRAM migration into SVM fault and prefetch paths

 drivers/gpu/drm/amd/amdgpu/Kconfig            |  10 +
 drivers/gpu/drm/amd/amdgpu/Makefile           |  11 +
 drivers/gpu/drm/amd/amdgpu/amdgpu.h           |   8 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c    |   2 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c       |   2 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c   | 848 +++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h   | 102 ++
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.c    |   4 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_reset.c     |   2 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm.c       | 724 +++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm.h       | 197 ++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_attr.c  | 972 ++++++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_attr.h  | 171 +++
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_fault.c | 418 ++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_fault.h |  39 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_range.c | 809 +++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_range.h | 167 +++
 .../drm/amd/amdgpu/amdgpu_svm_range_migrate.c | 120 +++
 .../drm/amd/amdgpu/amdgpu_svm_range_migrate.h |  35 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c       |  20 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c        |  23 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h        |   4 +
 include/uapi/drm/amdgpu_drm.h                 | 106 ++
 23 files changed, 4791 insertions(+), 3 deletions(-)
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.c
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_migrate.h
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm.c
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm.h
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_attr.c
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_attr.h
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_fault.c
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_fault.h
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_range.c
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_range.h
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_range_migrate.c
 create mode 100644 drivers/gpu/drm/amd/amdgpu/amdgpu_svm_range_migrate.h

-- 
2.53.0