From c4126f1db36e6b2e1c79b0e30a8a2de91c568f4c Mon Sep 17 00:00:00 2001 From: Arvind Yadav Date: Mon, 10 Aug 2026 14:58:45 +0530 Subject: drm/pagemap: Prevent double migration of device pages MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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] [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] Fixes: 99624bdff867 ("drm/gpusvm: Add support for GPU Shared Virtual Memory") Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Matthew Brost Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: Thomas Hellström Cc: Himal Prasad Ghimiray Assisted-by: Claude:claude-opus-4-8 Suggested-by: Matthew Brost Signed-off-by: Arvind Yadav Reviewed-by: Matthew Brost Signed-off-by: Matthew Brost Link: https://patch.msgid.link/20260810092845.2776097-1-arvind.yadav@intel.com --- include/drm/drm_pagemap.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h index 95eb4b66b057..ebbd3b0ddf36 100644 --- a/include/drm/drm_pagemap.h +++ b/include/drm/drm_pagemap.h @@ -2,6 +2,7 @@ #ifndef _DRM_PAGEMAP_H_ #define _DRM_PAGEMAP_H_ +#include #include #include #include @@ -339,6 +340,9 @@ struct drm_pagemap_migrate_details { #if IS_ENABLED(CONFIG_ZONE_DEVICE) +#define DRM_PAGEMAP_ZDD_FLAG_MIGRATED BIT(0) +#define DRM_PAGEMAP_ZDD_FLAG_MASK DRM_PAGEMAP_ZDD_FLAG_MIGRATED + int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation, struct mm_struct *mm, unsigned long start, unsigned long end, @@ -373,7 +377,9 @@ static inline struct drm_pagemap_zdd *drm_pagemap_page_zone_device_data(struct p { struct folio *folio = page_folio(page); - return folio_zone_device_data(folio); + return (struct drm_pagemap_zdd *) + ((unsigned long)folio_zone_device_data(folio) & + ~DRM_PAGEMAP_ZDD_FLAG_MASK); } #else -- cgit