kernel/git/stable/linux.git/mm/migrate_device.c, branch linux-7.2.y

mm/migrate_device: avoid out-of-bounds writes for compound folios

2026-09-11T09:50:56+00:00

commit dc41e961a269f2ca4196e669d6d8e05480899cd4 upstream. migrate_device_range() and migrate_device_pfns() clear the entries following a compound folio so that the PFN arrays retain their page-granular representation. If a compound folio extends beyond the end of the caller-provided range, the loops clear all following folio entries without limiting them to the number of slots remaining in the npages-sized array, causing an out-of-bounds write. Do not proceed with a compound folio if its page-granular representation does not fit entirely in the remaining PFN array. If this happens, drop any reference and lock acquired for the folio, clear the remaining entries, and stop collecting. Observed with a KASAN x86 QEMU kernel using the HMM migrate_anon_huge_zero selftest. Closing /dev/hmm_dmirror0 after migrating an anonymous huge page to device memory exercises: dmirror_fops_release() -> dmirror_device_evict_chunk() -> migrate_device_range() Link: https://lore.kernel.org/20260817120758.669807-3-sh_def@163.com Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages") Signed-off-by: Hui Su Cc: Alistair Popple Cc: Balbir Singh Cc: Byungchul Park Cc: David Hildenbrand Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Zi Yan Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

mm/migrate_device: clear stale mapping after freeing swapcache

2026-09-07T15:36:34+00:00

commit 34a00895d032a414830d41106a09329ae6c251b6 upstream. __migrate_device_pages() reads the folio mapping before calling folio_free_swap(). When folio_free_swap() succeeds, the folio is removed from the swap cache, but the saved mapping still points to swap_space. Passing the stale mapping to folio_migrate_mapping() makes it use the mapped-folio path for a folio that is no longer in swapcache. It can then operate on swap_space.i_pages with invalid reference accounting, eventually triggering a folio reference count BUG. After a successful split, nr still contains the number of pages in the original large folio, although each resulting page is now a separate order-0 folio. Reset nr to 1 so each split folio is processed separately, including its own swapcache removal and mapping lookup. Refresh the saved mapping after folio_free_swap() so the current folio state is used during migration. Link: https://lore.kernel.org/20260728062832.1107127-1-arvind.yadav@intel.com Fixes: df263d9a7dff ("mm/migrate_device: try to handle swapcache pages") Signed-off-by: Arvind Yadav Reviewed-by: Zi Yan Reviewed-by: Balbir Singh Cc: David Hildenbrand Cc: Matthew Brost Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE

2026-07-21T00:41:27+00:00

pte_pfn() and pte_dirty() have undefined behaviour when called on a non-present PTE. In migrate_vma_collect_pmd(), these functions may be invoked on non-present entries (e.g., device-private entries), leading to potential crashes from pte_pfn() or incorrect dirty folio accounting from pte_dirty(). Fix both by guarding with pte_present() checks. Link: https://lore.kernel.org/20260708003955.4024340-1-wangkefeng.wang@huawei.com Link: https://lore.kernel.org/20260706111958.3649651-1-wangkefeng.wang@huawei.com Fixes: fd35ca3d12cc ("mm/migrate_device.c: copy pte dirty bit to page") Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive") Signed-off-by: Kefeng Wang Reviewed-by: Balbir Singh Acked-by: Zi Yan Cc: Alistair Popple Cc: Byungchul Park Cc: David Hildenbrand Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Ying Huang Cc: Signed-off-by: Andrew Morton

mm/migrate_device: cleanup up PMD Checks and warnings

2026-05-29T04:04:47+00:00

Remove the odd VM_WARN_ON_FOLIO(!folio, folio) usage and replace it with a simpler VM_WARN_ON_ONCE(!folio) check. Drop the redundant VM_WARN_ON_ONCE(!pmd_none(*pmdp) && !is_huge_zero_pmd(*pmdp)). Refactor the PMD checks, making the control flow clearer and avoiding duplicate condition checks. Link: https://lore.kernel.org/20260419174747.10701-1-nueralspacetech@gmail.com Signed-off-by: Sunny Patel Acked-by: Zi Yan Reviewed-by: Huang Ying Acked-by: David Hildenbrand (Arm) Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Signed-off-by: Andrew Morton

mm/migrate_device: fix pgtable leak in migrate_vma_insert_huge_pmd_page

2026-05-22T02:06:13+00:00

When migrate_vma_insert_huge_pmd_page() jumps to unlock_abort due to a PMD check failure, the pgtable allocated earlier via pte_alloc_one() is never freed, causing a memory leak. Added free_abort label to release the pgtable in error path. Link: https://lore.kernel.org/20260501115122.23288-1-nueralspacetech@gmail.com Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages") Signed-off-by: Sunny Patel Acked-by: David Hildenbrand (Arm) Reviewed-by: Huang Ying Cc: Alistair Popple Cc: Balbir Singh Cc: Byungchul Park Cc: Gregory Price Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Zi Yan Cc: Signed-off-by: Andrew Morton

mm/migrate_device: fix spinlock leak in migrate_vma_insert_huge_pmd_page

2026-05-14T00:40:00+00:00

When check_stable_address_space() fails after the PMD spinlock has been acquired via pmd_lock(), the code jumps directly to the abort label, bypassing the spin_unlock() call in unlock_abort. This causes the PMD spinlock to be permanently held, leading to a deadlock. Change the goto target from abort to unlock_abort to ensure the spinlock is always released on this error path. Link: https://lore.kernel.org/20260425133537.17463-1-nueralspacetech@gmail.com Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages") Signed-off-by: Sunny Patel Reviewed-by: Andrew Morton Acked-by: Zi Yan Acked-by: Balbir Singh Acked-by: David Hildenbrand (Arm) Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Signed-off-by: Andrew Morton

mm/migrate_device: remove dead migration entry check in migrate_vma_collect_huge_pmd()

2026-04-18T07:10:56+00:00

The softleaf_is_migration() check is unreachable as entries that are not device_private are filtered out. Similarly, the PTE-level equivalent in migrate_vma_collect_pmd() skips migration entries. This dead branch also contained a double spin_unlock(ptl) bug. Link: https://lore.kernel.org/20260212014611.416695-1-dave@stgolabs.net Fixes: a30b48bf1b244 ("mm/migrate_device: implement THP migration of zone device pages") Signed-off-by: Davidlohr Bueso Suggested-by: Matthew Brost Reviewed-by: Alistair Popple Acked-by: Balbir Singh Acked-by: David Hildenbrand (Arm) Cc: Byungchul Park Cc: Gregory Price Cc: Jason Gunthorpe Cc: John Hubbard Cc: Joshua Hahn Cc: Mathew Brost Cc: Rakie Kim Cc: Ying Huang Cc: Zi Yan Cc: Thomas Hellström Signed-off-by: Andrew Morton

mm/migrate_device: document folio_get requirement before frozen PMD split

2026-04-05T20:53:19+00:00

split_huge_pmd_address() with freeze=true splits a PMD migration entry into PTE migration entries, consuming one folio reference in the process. The folio_get() before it provides this reference. Add a comment explaining this relationship. The expected folio refcount at the start of migrate_vma_split_unmapped_folio() is 1. Link: https://lkml.kernel.org/r/20260309212502.3922825-1-usama.arif@linux.dev Signed-off-by: Usama Arif Suggested-by: Zi Yan Reviewed-by: Zi Yan Reviewed-by: Nico Pache Acked-by: David Hildenbrand (Arm) Reviewed-by: Wei Yang Cc: Alistair Popple Cc: Byungchul Park Cc: Gregory Price Cc: "Huang, Ying" Cc: Johannes Weiner Cc: Joshua Hahn Cc: Matthew Brost Cc: Rakie Kim Cc: Ying Huang Signed-off-by: Andrew Morton

mm: Fix a hmm_range_fault() livelock / starvation problem

2026-03-02T16:51:51+00:00

If hmm_range_fault() fails a folio_trylock() in do_swap_page, trying to acquire the lock of a device-private folio for migration, to ram, the function will spin until it succeeds grabbing the lock. However, if the process holding the lock is depending on a work item to be completed, which is scheduled on the same CPU as the spinning hmm_range_fault(), that work item might be starved and we end up in a livelock / starvation situation which is never resolved. This can happen, for example if the process holding the device-private folio lock is stuck in migrate_device_unmap()->lru_add_drain_all() sinc lru_add_drain_all() requires a short work-item to be run on all online cpus to complete. A prerequisite for this to happen is: a) Both zone device and system memory folios are considered in migrate_device_unmap(), so that there is a reason to call lru_add_drain_all() for a system memory folio while a folio lock is held on a zone device folio. b) The zone device folio has an initial mapcount > 1 which causes at least one migration PTE entry insertion to be deferred to try_to_migrate(), which can happen after the call to lru_add_drain_all(). c) No or voluntary only preemption. This all seems pretty unlikely to happen, but indeed is hit by the "xe_exec_system_allocator" igt test. Resolve this by waiting for the folio to be unlocked if the folio_trylock() fails in do_swap_page(). Rename migration_entry_wait_on_locked() to softleaf_entry_wait_unlock() and update its documentation to indicate the new use-case. Future code improvements might consider moving the lru_add_drain_all() call in migrate_device_unmap() to be called *after* all pages have migration entries inserted. That would eliminate also b) above. v2: - Instead of a cond_resched() in hmm_range_fault(), eliminate the problem by waiting for the folio to be unlocked in do_swap_page() (Alistair Popple, Andrew Morton) v3: - Add a stub migration_entry_wait_on_locked() for the !CONFIG_MIGRATION case. (Kernel Test Robot) v4: - Rename migrate_entry_wait_on_locked() to softleaf_entry_wait_on_locked() and update docs (Alistair Popple) v5: - Add a WARN_ON_ONCE() for the !CONFIG_MIGRATION version of softleaf_entry_wait_on_locked(). - Modify wording around function names in the commit message (Andrew Morton) Suggested-by: Alistair Popple Fixes: 1afaeb8293c9 ("mm/migrate: Trylock device page in do_swap_page") Cc: Ralph Campbell Cc: Christoph Hellwig Cc: Jason Gunthorpe Cc: Jason Gunthorpe Cc: Leon Romanovsky Cc: Andrew Morton Cc: Matthew Brost Cc: John Hubbard Cc: Alistair Popple Cc: linux-mm@kvack.org Cc: Signed-off-by: Thomas Hellström Cc: # v6.15+ Reviewed-by: John Hubbard #v3 Reviewed-by: Alistair Popple Link: https://patch.msgid.link/20260210115653.92413-1-thomas.hellstrom@linux.intel.com (cherry picked from commit a69d1ab971a624c6f112cea61536569d579c3215) Signed-off-by: Rodrigo Vivi

mm: fix minor spelling mistakes in comments

2026-01-21T03:24:48+00:00

Correct several typos in comments across files in mm/ [akpm@linux-foundation.org: also fix comment grammar, per SeongJae] Link: https://lkml.kernel.org/r/20251218150906.25042-1-klourencodev@gmail.com Signed-off-by: Kevin Lourenco Reviewed-by: SeongJae Park Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Lorenzo Stoakes Signed-off-by: Andrew Morton