kernel/linux.git/mm/userfaultfd.c, branch v6.18.21

mm: fix some typos in mm module

2026-01-30T09:32:28+00:00

[ Upstream commit b6c46600bfb28b4be4e9cff7bad4f2cf357e0fb7 ] Below are some typos in the code comments: intevals ==> intervals addesses ==> addresses unavaliable ==> unavailable facor ==> factor droping ==> dropping exlusive ==> exclusive decription ==> description confict ==> conflict desriptions ==> descriptions otherwize ==> otherwise vlaue ==> value cheching ==> checking exisitng ==> existing modifed ==> modified differenciate ==> differentiate refernece ==> reference permissons ==> permissions indepdenent ==> independent spliting ==> splitting Just fix it. Link: https://lkml.kernel.org/r/20250929002608.1633825-1-jianyungao89@gmail.com Signed-off-by: jianyun.gao Reviewed-by: SeongJae Park Reviewed-by: Wei Yang Reviewed-by: Dev Jain Reviewed-by: Liam R. Howlett Acked-by: Chris Li Signed-off-by: Andrew Morton Stable-dep-of: 3937027caecb ("mm/hugetlb: fix two comments related to huge_pmd_unshare()") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

mm, swap: use unified helper for swap cache look up

2025-09-21T21:22:22+00:00

The swap cache lookup helper swap_cache_get_folio currently does readahead updates as well, so callers that are not doing swapin from any VMA or mapping are forced to reuse filemap helpers instead, and have to access the swap cache space directly. So decouple readahead update with swap cache lookup. Move the readahead update part into a standalone helper. Let the caller call the readahead update helper if they do readahead. And convert all swap cache lookups to use swap_cache_get_folio. After this commit, there are only three special cases for accessing swap cache space now: huge memory splitting, migration, and shmem replacing, because they need to lock the XArray. The following commits will wrap their accesses to the swap cache too, with special helpers. And worth noting, currently dropbehind is not supported for anon folio, and we will never see a dropbehind folio in swap cache. The unified helper can be updated later to handle that. While at it, add proper kernedoc for touched helpers. No functional change. Link: https://lkml.kernel.org/r/20250916160100.31545-3-ryncsn@gmail.com Signed-off-by: Kairui Song Reviewed-by: Baolin Wang Reviewed-by: Barry Song Acked-by: David Hildenbrand Acked-by: Chris Li Acked-by: Nhat Pham Suggested-by: Chris Li Cc: Baoquan He Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Johannes Weiner Cc: Kemeng Shi Cc: kernel test robot Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Yosry Ahmed Cc: Zi Yan Cc: SeongJae Park Signed-off-by: Andrew Morton

userfaultfd: opportunistic TLB-flush batching for present pages in MOVE

2025-09-13T23:55:00+00:00

MOVE ioctl's runtime is dominated by TLB-flush cost, which is required for moving present pages. Mitigate this cost by opportunistically batching present contiguous pages for TLB flushing. Without batching, in our testing on an arm64 Android device with UFFD GC, which uses MOVE ioctl for compaction, we observed that out of the total time spent in move_pages_pte(), over 40% is in ptep_clear_flush(), and ~20% in vm_normal_folio(). With batching, the proportion of vm_normal_folio() increases to over 70% of move_pages_pte() without any changes to vm_normal_folio(). Furthermore, time spent within move_pages_pte() is only ~20%, which includes TLB-flush overhead. When the GC intensive benchmark, which was used to gather the above numbers, is run on cuttlefish (qemu android instance on x86_64), the completion time of the benchmark went down from ~45mins to ~20mins. Furthermore, system_server, one of the most performance critical system processes on android, saw over 50% reduction in GC compaction time on an arm64 android device. [lokeshgidra@google.com: make calculation of largest extent that can be batched unconditional on length, per Barry] Link: https://lkml.kernel.org/r/20250816191123.3601561-1-lokeshgidra@google.com Link: https://lkml.kernel.org/r/20250813193024.2279805-1-lokeshgidra@google.com Signed-off-by: Lokesh Gidra Acked-by: Peter Xu Reviewed-by: Barry Song Cc: Suren Baghdasaryan Cc: Kalesh Singh Cc: David Hildenbrand Signed-off-by: Andrew Morton

mm/userfaultfd: fix kmap_local LIFO ordering for CONFIG_HIGHPTE

2025-08-28T05:45:41+00:00

With CONFIG_HIGHPTE on 32-bit ARM, move_pages_pte() maps PTE pages using kmap_local_page(), which requires unmapping in Last-In-First-Out order. The current code maps dst_pte first, then src_pte, but unmaps them in the same order (dst_pte, src_pte), violating the LIFO requirement. This causes the warning in kunmap_local_indexed(): WARNING: CPU: 0 PID: 604 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c addr \!= __fix_to_virt(FIX_KMAP_BEGIN + idx) Fix this by reversing the unmap order to respect LIFO ordering. This issue follows the same pattern as similar fixes: - commit eca6828403b8 ("crypto: skcipher - fix mismatch between mapping and unmapping order") - commit 8cf57c6df818 ("nilfs2: eliminate staggered calls to kunmap in nilfs_rename") Both of which addressed the same fundamental requirement that kmap_local operations must follow LIFO ordering. Link: https://lkml.kernel.org/r/20250731144431.773923-1-sashal@kernel.org Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Signed-off-by: Sasha Levin Acked-by: David Hildenbrand Reviewed-by: Suren Baghdasaryan Cc: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton

userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry

2025-08-12T06:00:59+00:00

When UFFDIO_MOVE encounters a migration PMD entry, it proceeds with obtaining a folio and accessing it even though the entry is swp_entry_t. Add the missing check and let split_huge_pmd() handle migration entries. While at it also remove unnecessary folio check. [surenb@google.com: remove extra folio check, per David] Link: https://lkml.kernel.org/r/20250807200418.1963585-1-surenb@google.com Link: https://lkml.kernel.org/r/20250806220022.926763-1-surenb@google.com Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Signed-off-by: Suren Baghdasaryan Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ Reviewed-by: Peter Xu Acked-by: David Hildenbrand Cc: Andrea Arcangeli Cc: Lokesh Gidra Cc: Signed-off-by: Andrew Morton

mm: remove redundant pXd_devmap calls

2025-07-10T05:42:17+00:00

DAX was the only thing that created pmd_devmap and pud_devmap entries however it no longer does as DAX pages are now refcounted normally and pXd_trans_huge() returns true for those. Therefore checking both pXd_devmap and pXd_trans_huge() is redundant and the former can be removed without changing behaviour as it will always be false. Link: https://lkml.kernel.org/r/d58f089dc16b7feb7c6728164f37dea65d64a0d3.1750323463.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple Cc: Balbir Singh Cc: Björn Töpel Cc: Björn Töpel Cc: Christoph Hellwig Cc: Chunyan Zhang Cc: Dan Williams Cc: David Hildenbrand Cc: Deepak Gupta Cc: Gerald Schaefer Cc: Inki Dae Cc: Jason Gunthorpe Cc: John Groves Cc: John Hubbard Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Will Deacon Signed-off-by: Andrew Morton

mm: convert pXd_devmap checks to vma_is_dax

2025-07-10T05:42:15+00:00

Patch series "mm: Remove pXX_devmap page table bit and pfn_t type", v3. All users of dax now require a ZONE_DEVICE page which is properly refcounted. This means there is no longer any need for the PFN_DEV, PFN_MAP and PFN_SPECIAL flags. Furthermore the PFN_SG_CHAIN and PFN_SG_LAST flags never appear to have been used. It is therefore possible to remove the pfn_t type and replace any usage with raw pfns. The remaining users of PFN_DEV have simply passed this to vmf_insert_mixed() to create pte_devmap() mappings. It is unclear why this was the case but presumably to ensure vm_normal_page() does not return these pages. These users can be trivially converted to raw pfns and creating a pXX_special() mapping to ensure vm_normal_page() still doesn't return these pages. Now that there are no users of PFN_DEV we can remove the devmap page table bit and all associated functions and macros, freeing up a software page table bit. This patch (of 14): Currently dax is the only user of pmd and pud mapped ZONE_DEVICE pages. Therefore page walkers that want to exclude DAX pages can check pmd_devmap or pud_devmap. However soon dax will no longer set PFN_DEV, meaning dax pages are mapped as normal pages. Ensure page walkers that currently use pXd_devmap to skip DAX pages continue to do so by adding explicit checks of the VMA instead. Remove vma_is_dax() check from mm/userfaultfd.c as validate_move_areas() will already skip DAX VMA's on account of them not being anonymous. The check in userfaultfd_must_wait() is also redundant as vma_can_userfault() should have already filtered out dax vma's. For HMM the pud_devmap check seems unnecessary as there is no reason we shouldn't be able to handle any leaf PUD here so remove it also. Link: https://lkml.kernel.org/r/cover.176965585864cb8d2cf41464b44dcc0471e643a0.1750323463.git-series.apopple@nvidia.com Link: https://lkml.kernel.org/r/f0611f6f475f48fcdf34c65084a359aefef4cccc.1750323463.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple Reviewed-by: Jason Gunthorpe Reviewed-by: Dan Williams Cc: Balbir Singh Cc: Björn Töpel Cc: Christoph Hellwig Cc: Chunyan Zhang Cc: David Hildenbrand Cc: Deepak Gupta Cc: Gerald Schaefer Cc: Inki Dae Cc: John Groves Cc: John Hubbard Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Björn Töpel Cc: Will Deacon Signed-off-by: Andrew Morton

mm: update core kernel code to use vm_flags_t consistently

2025-07-10T05:42:13+00:00

The core kernel code is currently very inconsistent in its use of vm_flags_t vs. unsigned long. This prevents us from changing the type of vm_flags_t in the future and is simply not correct, so correct this. While this results in rather a lot of churn, it is a critical pre-requisite for a future planned change to VMA flag type. Additionally, update VMA userland tests to account for the changes. To make review easier and to break things into smaller parts, driver and architecture-specific changes is left for a subsequent commit. The code has been adjusted to cascade the changes across all calling code as far as is needed. We will adjust architecture-specific and driver code in a subsequent patch. Overall, this patch does not introduce any functional change. Link: https://lkml.kernel.org/r/d1588e7bb96d1ea3fe7b9df2c699d5b4592d901d.1750274467.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Acked-by: Kees Cook Acked-by: Mike Rapoport (Microsoft) Acked-by: Jan Kara Acked-by: Christian Brauner Reviewed-by: Vlastimil Babka Acked-by: Oscar Salvador Reviewed-by: Pedro Falcato Acked-by: Zi Yan Acked-by: David Hildenbrand Reviewed-by: Anshuman Khandual Cc: Jann Horn Cc: Liam R. Howlett Cc: Catalin Marinas Cc: Jarkko Sakkinen Signed-off-by: Andrew Morton

userfaultfd: remove (VM_)BUG_ON()s

2025-07-10T05:42:01+00:00

BUG_ON() is deprecated [1]. Convert all the BUG_ON()s and VM_BUG_ON()s to use VM_WARN_ON_ONCE(). There are a few additional cases that are converted or modified: - Convert the printk(KERN_WARNING ...) in handle_userfault() to use pr_warn(). - Convert the WARN_ON_ONCE()s in move_pages() to use VM_WARN_ON_ONCE(), as the relevant conditions are already checked in validate_range() in move_pages()'s caller. - Convert the VM_WARN_ON()'s in move_pages() to VM_WARN_ON_ONCE(). These cases should never happen and are similar to those in mfill_atomic() and mfill_atomic_hugetlb(), which were previously BUG_ON()s. move_pages() was added later than those functions and makes use of VM_WARN_ON() as a replacement for the deprecated BUG_ON(), but. VM_WARN_ON_ONCE() is likely a better direct replacement. - Convert the WARN_ON() for !VM_MAYWRITE in userfaultfd_unregister() and userfaultfd_register_range() to VM_WARN_ON_ONCE(). This condition is enforced in userfaultfd_register() so it should never happen, and can be converted to a debug check. [1] https://www.kernel.org/doc/html/v6.15/process/coding-style.html#use-warn-rather-than-bug Link: https://lkml.kernel.org/r/20250619-uffd-fixes-v3-3-a7274d3bd5e4@columbia.edu Signed-off-by: Tal Zussman Cc: Al Viro Cc: Andrea Arcangeli Cc: Christian Brauner Cc: David Hildenbrand Cc: Jan Kara Cc: Jason A. Donenfeld Cc: Peter Xu Signed-off-by: Andrew Morton

mm: userfaultfd: fix race of userfaultfd_move and swap cache

2025-06-20T03:48:01+00:00

This commit fixes two kinds of races, they may have different results: Barry reported a BUG_ON in commit c50f8e6053b0, we may see the same BUG_ON if the filemap lookup returned NULL and folio is added to swap cache after that. If another kind of race is triggered (folio changed after lookup) we may see RSS counter is corrupted: [ 406.893936] BUG: Bad rss-counter state mm:ffff0000c5a9ddc0 type:MM_ANONPAGES val:-1 [ 406.894071] BUG: Bad rss-counter state mm:ffff0000c5a9ddc0 type:MM_SHMEMPAGES val:1 Because the folio is being accounted to the wrong VMA. I'm not sure if there will be any data corruption though, seems no. The issues above are critical already. On seeing a swap entry PTE, userfaultfd_move does a lockless swap cache lookup, and tries to move the found folio to the faulting vma. Currently, it relies on checking the PTE value to ensure that the moved folio still belongs to the src swap entry and that no new folio has been added to the swap cache, which turns out to be unreliable. While working and reviewing the swap table series with Barry, following existing races are observed and reproduced [1]: In the example below, move_pages_pte is moving src_pte to dst_pte, where src_pte is a swap entry PTE holding swap entry S1, and S1 is not in the swap cache: CPU1 CPU2 userfaultfd_move move_pages_pte() entry = pte_to_swp_entry(orig_src_pte); // Here it got entry = S1 ... < interrupted> ... // folio A is a new allocated folio // and get installed into src_pte // src_pte now points to folio A, S1 // has swap count == 0, it can be freed // by folio_swap_swap or swap // allocator's reclaim. // folio B is a folio in another VMA. // S1 is freed, folio B can use it // for swap out with no problem. ... folio = filemap_get_folio(S1) // Got folio B here !!! ... < interrupted again> ... // Now S1 is free to be used again. // Now src_pte is a swap entry PTE // holding S1 again. folio_trylock(folio) move_swap_pte double_pt_lock is_pte_pages_stable // Check passed because src_pte == S1 folio_move_anon_rmap(...) // Moved invalid folio B here !!! The race window is very short and requires multiple collisions of multiple rare events, so it's very unlikely to happen, but with a deliberately constructed reproducer and increased time window, it can be reproduced easily. This can be fixed by checking if the folio returned by filemap is the valid swap cache folio after acquiring the folio lock. Another similar race is possible: filemap_get_folio may return NULL, but folio (A) could be swapped in and then swapped out again using the same swap entry after the lookup. In such a case, folio (A) may remain in the swap cache, so it must be moved too: CPU1 CPU2 userfaultfd_move move_pages_pte() entry = pte_to_swp_entry(orig_src_pte); // Here it got entry = S1, and S1 is not in swap cache folio = filemap_get_folio(S1) // Got NULL ... < interrupted again> ... move_swap_pte double_pt_lock is_pte_pages_stable // Check passed because src_pte == S1 folio_move_anon_rmap(...) // folio A is ignored !!! Fix this by checking the swap cache again after acquiring the src_pte lock. And to avoid the filemap overhead, we check swap_map directly [2]. The SWP_SYNCHRONOUS_IO path does make the problem more complex, but so far we don't need to worry about that, since folios can only be exposed to the swap cache in the swap out path, and this is covered in this patch by checking the swap cache again after acquiring the src_pte lock. Testing with a simple C program that allocates and moves several GB of memory did not show any observable performance change. Link: https://lkml.kernel.org/r/20250604151038.21968-1-ryncsn@gmail.com Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") Signed-off-by: Kairui Song Closes: https://lore.kernel.org/linux-mm/CAMgjq7B1K=6OOrK2OUZ0-tqCzi+EJt+2_K97TPGoSt=9+JwP7Q@mail.gmail.com/ [1] Link: https://lore.kernel.org/all/CAGsJ_4yJhJBo16XhiC-nUzSheyX-V3-nFE+tAi=8Y560K8eT=A@mail.gmail.com/ [2] Reviewed-by: Lokesh Gidra Acked-by: Peter Xu Reviewed-by: Suren Baghdasaryan Reviewed-by: Barry Song Reviewed-by: Chris Li Cc: Andrea Arcangeli Cc: David Hildenbrand Cc: Kairui Song Cc: Signed-off-by: Andrew Morton