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c4126f1db3
A device-private folio migrated to system memory by a CPU fault can
remain reachable through the raw-PFN eviction path until migration
finalization drops the source reference.
If eviction selects the same device-private folio during this window,
it can attempt to migrate the folio again. The second migration can leave
an uncharged folio on an LRU list, causing folio_lruvec_lock_irqsave() to
retry indefinitely and resulting in a soft lockup and RCU stall.
Mark successfully migrated device-private folios using a low bit of
their zone_device_data before migration finalization. Make both CPU-fault
and raw-PFN migration paths skip device-private folios carrying this
flag.
Mask the flag when retrieving the drm_pagemap_zdd pointer and preserve
it when a device-private folio is split. Keeping the state on the physical
folio also avoids depending on a virtual address that may change before a
fault occurs.
v2:
- Replace the retired-PFN XArray with an embedded bitmap. (Matthew Brost)
- Mark every base page covered by a migrated folio so retirement remains
valid if the folio is later split.
v3:
- Store the migrated state in a low bit of zone_device_data instead of
adding virtual-range and bitmap tracking to the ZDD. (Matthew Brost)
- Mask the flag when retrieving the ZDD and preserve it when splitting
a folio.
- Drop the pre-existing fixes already covered by Matthew Brost's series:
https://patchwork.freedesktop.org/series/171651/
v4:
- Advance by the folio size only for migration entries marked with
MIGRATE_PFN_COMPOUND. (Sashiko)
v5:
- Simplify ZDD flag updates and folio iteration. (Matthew Brost)
- Skip retired device-private folios in the CPU-fault path. (Matthew Brost)
- Preserve flag bits while taking a new ZDD reference for split folios.
v6:
- Restore MIGRATE_PFN_COMPOUND-aware stepping so non-compound migration
entries are processed one at a time. (Sashiko)
- Drop the pre-existing fixes already covered by Matthew Brost's series:
https://patchwork.freedesktop.org/series/171651/
The lockup was observed as:
[10109.860465] watchdog: BUG: soft lockup - CPU#9 stuck for 26s! [kworker/u65:5:6557]
[10109.860524] Tainted: [S]=CPU_OUT_OF_SPEC, [O]=OOT_MODULE
[10109.860524] Hardware name: ASUS System Product Name/PRIME Z790-P WIFI, BIOS 0812 02/24/2023
[10109.860525] Workqueue: xe_page_fault_work_queue xe_pagefault_queue_work [xe]
[10109.860644] RIP: 0010:_raw_spin_unlock_irqrestore+0x57/0x80
[10109.860655] Call Trace:
[10109.860655] <TASK>
[10109.860657] folio_lruvec_lock_irqsave+0x216/0x220
[10109.860661] ? __pfx_lru_add+0x10/0x10
[10109.860665] folio_batch_move_lru+0xc8/0x450
[10109.860670] ? lock_acquire+0xc4/0x2d0
[10109.860674] ? __folio_batch_add_and_move+0x60/0x2e0
[10109.860677] ? folio_migrate_mapping+0xa6/0x110
[10109.860679] ? folio_migrate_flags+0x13b/0x1b0
[10109.860681] ? __pfx_lru_add+0x10/0x10
[10109.860683] __folio_batch_add_and_move+0xe7/0x2e0
[10109.860685] ? dma_iova_try_alloc+0xb0/0x140
[10109.860689] folio_add_lru+0x64/0x80
[10109.860691] __migrate_device_finalize+0x12c/0x270
[10109.860695] migrate_device_finalize+0x10/0x20
[10109.860698] drm_pagemap_evict_to_ram+0x185/0x370 [drm_gpusvm_helper]
[10109.860704] ? drm_pagemap_evict_to_ram+0x96/0x370 [drm_gpusvm_helper]
[10109.860709] xe_svm_bo_evict+0x15/0x20 [xe]
[10109.860819] ? xe_svm_bo_evict+0x15/0x20 [xe]
[10109.860921] xe_bo_move+0x107e/0x1570 [xe]
[10109.860992] ? xe_ttm_tt_create+0x168/0x340 [xe]
[10109.861059] ? __up_read+0x98/0x2b0
[10109.861061] ? lock_is_held_type+0xa3/0x130
[10109.861067] ttm_bo_handle_move_mem+0xe8/0x1e0 [ttm]
[10109.861075] ttm_bo_evict+0x141/0x1c0 [ttm]
[10109.861081] ttm_bo_evict_cb+0x9f/0x100 [ttm]
[10109.861086] ttm_lru_walk_for_evict+0x84/0x190 [ttm]
[10109.861091] ? xe_ttm_vram_mgr_new+0x258/0x3a0 [xe]
[10109.861198] ttm_bo_alloc_resource+0x219/0x750 [ttm]
[10109.861203] ? ttm_bo_alloc_resource+0xa9/0x750 [ttm]
[10109.861208] ? lock_acquire+0xc4/0x2d0
[10109.861214] ttm_bo_validate+0x94/0x1c0 [ttm]
[10109.861218] ? ww_mutex_trylock+0x19d/0x3d0
[10109.861219] ? _raw_write_unlock+0x22/0x50
[10109.861223] ttm_bo_init_reserved+0x17d/0x1f0 [ttm]
[10109.861228] xe_bo_init_locked+0x20a/0x620 [xe]
[10109.861294] ? __pfx_xe_ttm_bo_destroy+0x10/0x10 [xe]
[10109.861359] ? mark_held_locks+0x46/0x90
[10109.861361] ? __create_object+0x68/0xc0
[10109.861366] __xe_bo_create_locked+0x384/0xa20 [xe]
[10109.861432] ? lock_acquire+0xc4/0x2d0
[10109.861434] ? xe_drm_pagemap_populate_mm+0xd3/0x340 [xe]
[10109.861542] xe_bo_create_locked+0x23/0x40 [xe]
[10109.861609] xe_drm_pagemap_populate_mm+0x12e/0x340 [xe]
[10109.861707] ? __lock_acquire+0x43e/0x2930
[10109.861716] drm_pagemap_populate_mm+0x74/0xe0 [drm_gpusvm_helper]
[10109.861720] xe_svm_alloc_vram+0xb5/0x2c0 [xe]
[10109.861817] ? seqcount_lockdep_reader_access.constprop.0+0x9f/0xc0
[10109.861819] ? ktime_get+0x23/0x130
[10109.861821] ? trace_hardirqs_on+0x22/0xe0
[10109.861823] ? seqcount_lockdep_reader_access.constprop.0+0x9f/0xc0
[10109.861826] __xe_svm_handle_pagefault+0x77d/0xbf0 [xe]
[10109.861924] ? rwsem_down_write_slowpath+0x43a/0x9a0
[10109.861926] ? _raw_spin_unlock_irq+0x27/0x70
[10109.861928] ? rwsem_down_write_slowpath+0x43a/0x9a0
[10109.861929] ? trace_hardirqs_on+0x22/0xe0
[10109.861931] ? _raw_spin_unlock_irq+0x27/0x70
[10109.861933] ? rwsem_down_write_slowpath+0x459/0x9a0
[10109.861937] xe_svm_handle_pagefault+0x3d/0xb0 [xe]
[10109.862030] xe_pagefault_queue_work+0x1a9/0x520 [xe]
[10109.862122] process_one_work+0x239/0x730
[10109.862127] worker_thread+0x200/0x3f0
[10109.862130] ? __pfx_worker_thread+0x10/0x10
[10109.862132] kthread+0x10d/0x150
[10109.862133] ? __pfx_kthread+0x10/0x10
[10109.862135] ret_from_fork+0x3bd/0x470
[10109.862138] ? __pfx_kthread+0x10/0x10
[10109.862140] ret_from_fork_asm+0x1a/0x30
[10109.862146] </TASK>
Fixes: 99624bdff8 ("drm/gpusvm: Add support for GPU Shared Virtual Memory")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Assisted-by: Claude:claude-opus-4-8
Suggested-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260810092845.2776097-1-arvind.yadav@intel.com