Introduction ============ Some devices have features such as atomic PTE bits that can be used to implement atomic access to system memory. To support atomic operations to a shared virtual memory page such a device needs access to that page which is exclusive of the CPU. This series introduces a mechanism to temporarily unmap pages granting exclusive access to a device. These changes are required to support OpenCL atomic operations in Nouveau to shared virtual memory (SVM) regions allocated with the CL_MEM_SVM_ATOMICS clSVMAlloc flag. A more complete description of the OpenCL SVM feature is available at https://www.khronos.org/registry/OpenCL/specs/3.0-unified/html/ OpenCL_API.html#_shared_virtual_memory . Implementation ============== 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. Patches ======= Patches 1 & 2 refactor existing migration and device private entry functions. Patches 3 & 4 rework try_to_unmap_one() by splitting out unrelated functionality into separate functions - try_to_migrate_one() and try_to_munlock_one(). Patch 5 renames some existing code but does not introduce functionality. Patch 6 is a small clean-up to swap entry handling in copy_pte_range(). Patch 7 contains the bulk of the implementation for device exclusive memory. Patch 8 contains some additions to the HMM selftests to ensure everything works as expected. Patch 9 is a cleanup for the Nouveau SVM implementation. Patch 10 contains the implementation of atomic access for the Nouveau driver. Testing ======= This has been tested with upstream Mesa 21.1.0 and a simple OpenCL program which checks that GPU atomic accesses to system memory are atomic. Without this series the test fails as there is no way of write-protecting the page mapping which results in the device clobbering CPU writes. For reference the test is available at https://ozlabs.org/~apopple/opencl_svm_atomics/ Further testing has been performed by adding support for testing exclusive access to the hmm-tests kselftests. On Wednesday, 16 June 2021 8:59:27 PM AEST Alistair Popple wrote: Alistair Popple (10): mm: Remove special swap entry functions mm/swapops: Rework swap entry manipulation code mm/rmap: Split try_to_munlock from try_to_unmap mm/rmap: Split migration into its own function mm: Rename migrate_pgmap_owner mm/memory.c: Allow different return codes for copy_nonpresent_pte() mm: Device exclusive memory access mm: Selftests for exclusive device memory nouveau/svm: Refactor nouveau_range_fault nouveau/svm: Implement atomic SVM access Documentation/vm/hmm.rst | 19 +- Documentation/vm/unevictable-lru.rst | 33 +- arch/s390/mm/pgtable.c | 2 +- drivers/gpu/drm/nouveau/include/nvif/if000c.h | 1 + drivers/gpu/drm/nouveau/nouveau_svm.c | 156 ++++- drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.h | 1 + .../drm/nouveau/nvkm/subdev/mmu/vmmgp100.c | 6 + fs/proc/task_mmu.c | 23 +- include/linux/mmu_notifier.h | 26 +- include/linux/rmap.h | 11 +- include/linux/swap.h | 13 +- include/linux/swapops.h | 123 ++-- lib/test_hmm.c | 127 +++- lib/test_hmm_uapi.h | 2 + mm/debug_vm_pgtable.c | 12 +- mm/hmm.c | 12 +- mm/huge_memory.c | 48 +- mm/hugetlb.c | 10 +- mm/memcontrol.c | 2 +- mm/memory.c | 175 ++++- mm/migrate.c | 51 +- mm/mlock.c | 12 +- mm/mprotect.c | 18 +- mm/page_vma_mapped.c | 15 +- mm/rmap.c | 612 +++++++++++++++--- tools/testing/selftests/vm/hmm-tests.c | 158 +++++ 26 files changed, 1341 insertions(+), 327 deletions(-)
