linux-kernel - [PATCH v2 0/4] Add support for SVM atomics in Nouveau

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Date:   Fri, 19 Feb 2021 13:07:46 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     <linux-mm@...ck.org>, <nouveau@...ts.freedesktop.org>,
        <bskeggs@...hat.com>, <akpm@...ux-foundation.org>
CC:     <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kvm-ppc@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <jhubbard@...dia.com>, <rcampbell@...dia.com>,
        <jglisse@...hat.com>, <jgg@...dia.com>, <hch@...radead.org>,
        <daniel@...ll.ch>, Alistair Popple <apopple@...dia.com>
Subject: [PATCH v2 0/4] Add support for SVM atomics in Nouveau

This is the second version of a series to add support to Nouveau for atomic
memory operations on OpenCL shared virtual memory (SVM) regions. This is
achieved using the atomic PTE bits on the GPU to only permit atomic
operations to system memory when a page is not mapped in userspace on the
CPU. The previous version of this series used an unmap and pin page
migration, however this resulted in problems with ZONE_MOVABLE and other
issues so this series uses a different approach.

Instead exclusive device access is implemented by adding a new swap entry
type (SWAP_DEVICE_EXCLUSIVE) which is similar to a migration entry. The
main difference is that on fault the original entry is immediately restored
by the fault handler instead of waiting.

Restoring the entry triggers calls to MMU notifers which allows a device
driver to revoke the atomic access permission from the GPU prior to the CPU
finalising the entry.

Patch 1 contains the bulk of the memory management changes required to
implement the new entry type.

Patch 2 contains some additions to the HMM selftests to ensure everything
works as expected.

Patch 3 was posted previously and has not changed.

Patch 4 is similar to what was posted previously but updated to use the new
swap entries instread of migration.

This has been tested using the latest upstream Mesa userspace with a simple
OpenCL test program which checks the results of atomic GPU operations on a
SVM buffer whilst also writing to the same buffer from the CPU.

Alistair Popple (4):
  hmm: Device exclusive memory access
  hmm: Selftests for exclusive device memory
  nouveau/svm: Refactor nouveau_range_fault
  nouveau/svm: Implement atomic SVM access

 Documentation/vm/hmm.rst                      |  15 ++
 drivers/gpu/drm/nouveau/include/nvif/if000c.h |   1 +
 drivers/gpu/drm/nouveau/nouveau_svm.c         | 118 +++++++---
 drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h |   1 +
 .../drm/nouveau/nvkm/subdev/mmu/vmmgp100.c    |   6 +
 fs/proc/task_mmu.c                            |   7 +
 include/linux/hmm.h                           |   4 +
 include/linux/rmap.h                          |   1 +
 include/linux/swap.h                          |  10 +-
 include/linux/swapops.h                       |  32 +++
 lib/test_hmm.c                                | 124 ++++++++++
 lib/test_hmm_uapi.h                           |   2 +
 mm/hmm.c                                      | 206 ++++++++++++++++
 mm/memory.c                                   |  34 ++-
 mm/mprotect.c                                 |   7 +
 mm/page_vma_mapped.c                          |  14 +-
 mm/rmap.c                                     |  29 ++-
 tools/testing/selftests/vm/hmm-tests.c        | 219 ++++++++++++++++++
 18 files changed, 792 insertions(+), 38 deletions(-)

-- 
2.20.1