v9
2026-07-16
HMM支持userfaultfd时释放mmap锁 · v9
Stanislav Kinsburskii的v9 patch系列为HMM添加mmap锁释放支持，新增hmm_range_fault_unlocked_timeout()函数。
原始补丁链接
子 Patch（8）
1/8
mm/hmm: move page fault handling out of walk callbacks
hmm_range_fault() currently triggers page faults from inside the page-table walk callbacks: hmm_vma_walk_pmd(), hmm_vma_walk_pud(), hmm_vma_walk_hugetlb_entry() and the pte-level helper all call hmm_v
2/8
mm/hmm: add hmm_range_fault_unlocked_timeout() for mmap lock-drop support
hmm_range_fault() requires the caller to hold the mmap read lock for the duration of the call. This is incompatible with mappings whose fault handler may release the mmap lock, notably userfaultfd-man
3/8
selftests/mm: add HMM test for mmap lock-dropping faults
Add test_hmm coverage for the HMM lock-dropping fault path. The test module gets a new HMM_DMIRROR_READ_UNLOCKED ioctl that calls hmm_range_fault_unlocked_timeout() with a timeout of 0, exercising the
4/8
mshv: Use hmm_range_fault_unlocked_timeout() for region faults
MSHV currently faults movable memory regions by taking mmap_read_lock() around hmm_range_fault(). That prevents the fault path from handling VMAs whose fault handlers need to drop mmap_lock, such as u
5/8
drm/nouveau: Use hmm_range_fault_unlocked_timeout() for SVM faults
nouveau_range_fault() takes mmap_read_lock() only to call hmm_range_fault(). It also keeps a single HMM_RANGE_DEFAULT_TIMEOUT deadline across both HMM -EBUSY retries and post-fault mmu_interval_read_r
6/8
RDMA/umem: Use hmm_range_fault_unlocked_timeout() for ODP faults
ib_umem_odp_map_dma_and_lock() takes mmap_read_lock() only around hmm_range_fault(), then retries -EBUSY until HMM_RANGE_DEFAULT_TIMEOUT expires. Use hmm_range_fault_unlocked_timeout() instead. The H
7/8
accel/amdxdna: Use hmm_range_fault_unlocked_timeout() for range population
aie2_populate_range() takes mmap_read_lock() only around hmm_range_fault(). It also open-codes the mmu interval sequence setup before each HMM walk and retries -EBUSY until HMM_RANGE_DEFAULT_TIMEOUT e
8/8
drm/gpusvm: Use hmm_range_fault_unlocked_timeout() for range faults
Several GPU SVM paths take mmap_read_lock() only to call hmm_range_fault() and open-code mmu interval sequence setup before each HMM walk. They also retry -EBUSY until HMM_RANGE_DEFAULT_TIMEOUT expire