kernel/linux.git/mm/ksm.c, branch v7.1

mm: convert do_brk_flags() to use vma_flags_t

2026-04-05T20:53:40+00:00

In order to be able to do this, we need to change VM_DATA_DEFAULT_FLAGS and friends and update the architecture-specific definitions also. We then have to update some KSM logic to handle VMA flags, and introduce VMA_STACK_FLAGS to define the vma_flags_t equivalent of VM_STACK_FLAGS. We also introduce two helper functions for use during the time we are converting legacy flags to vma_flags_t values - vma_flags_to_legacy() and legacy_to_vma_flags(). This enables us to iteratively make changes to break these changes up into separate parts. We use these explicitly here to keep VM_STACK_FLAGS around for certain users which need to maintain the legacy vm_flags_t values for the time being. We are no longer able to rely on the simple VM_xxx being set to zero if the feature is not enabled, so in the case of VM_DROPPABLE we introduce VMA_DROPPABLE as the vma_flags_t equivalent, which is set to EMPTY_VMA_FLAGS if the droppable flag is not available. While we're here, we make the description of do_brk_flags() into a kdoc comment, as it almost was already. We use vma_flags_to_legacy() to not need to update the vm_get_page_prot() logic as this time. Note that in create_init_stack_vma() we have to replace the BUILD_BUG_ON() with a VM_WARN_ON_ONCE() as the tested values are no longer build time available. We also update mprotect_fixup() to use VMA flags where possible, though we have to live with a little duplication between vm_flags_t and vma_flags_t values for the time being until further conversions are made. While we're here, update VM_SPECIAL to be defined in terms of VMA_SPECIAL_FLAGS now we have vma_flags_to_legacy(). Finally, we update the VMA tests to reflect these changes. Link: https://lkml.kernel.org/r/d02e3e45d9a33d7904b149f5604904089fd640ae.1774034900.git.ljs@kernel.org Signed-off-by: Lorenzo Stoakes (Oracle) Acked-by: Paul Moore [SELinux] Acked-by: Vlastimil Babka (SUSE) Cc: Albert Ou Cc: Alexander Gordeev Cc: Alexandre Ghiti Cc: Al Viro Cc: Anton Ivanov Cc: "Borislav Petkov (AMD)" Cc: Catalin Marinas Cc: Chengming Zhou Cc: Christian Borntraeger Cc: Christian Brauner Cc: David Hildenbrand Cc: Dinh Nguyen Cc: Heiko Carstens Cc: "H. Peter Anvin" Cc: Huacai Chen Cc: Ingo Molnar Cc: Jan Kara Cc: Jann Horn Cc: Johannes Berg Cc: Kees Cook Cc: Liam Howlett Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Michal Hocko Cc: Mike Rapoport Cc: Nicholas Piggin Cc: Ondrej Mosnacek Cc: Palmer Dabbelt Cc: Pedro Falcato Cc: Richard Weinberger Cc: Russell King Cc: Stephen Smalley Cc: Suren Baghdasaryan Cc: Sven Schnelle Cc: Thomas Bogendoerfer Cc: Vasily Gorbik Cc: Vineet Gupta Cc: WANG Xuerui Cc: Will Deacon Cc: xu xin Signed-off-by: Andrew Morton

ksm: initialize the addr only once in rmap_walk_ksm

2026-04-05T20:52:35+00:00

This is a minor performance optimization, especially when there are many for-loop iterations, because the addr variable doesn't change across iterations. Therefore, it only needs to be initialized once before the loop. Link: https://lkml.kernel.org/r/20260212192820223O_r2NQzSEPG_C56cs-z4l@zte.com.cn Link: https://lkml.kernel.org/r/20260212192932941MSsJEAyoRW4YdLBN7_myn@zte.com.cn Signed-off-by: xu xin Acked-by: David Hildenbrand (Arm) Cc: Chengming Zhou Cc: Hugh Dickins Cc: Wang Yaxin Cc: Yang Yang Signed-off-by: Andrew Morton

Convert more 'alloc_obj' cases to default GFP_KERNEL arguments

2026-02-22T04:03:00+00:00

This converts some of the visually simpler cases that have been split over multiple lines. I only did the ones that are easy to verify the resulting diff by having just that final GFP_KERNEL argument on the next line. Somebody should probably do a proper coccinelle script for this, but for me the trivial script actually resulted in an assertion failure in the middle of the script. I probably had made it a bit _too_ trivial. So after fighting that far a while I decided to just do some of the syntactically simpler cases with variations of the previous 'sed' scripts. The more syntactically complex multi-line cases would mostly really want whitespace cleanup anyway. Signed-off-by: Linus Torvalds

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook

mm/ksm: fix pte_unmap_unlock of wrong address in break_ksm_pmd_entry

2025-12-23T19:23:17+00:00

On ARM32 with HIGHMEM/HIGHPTE, break_ksm_pmd_entry() triggers a BUG during KSM unmerging because pte_unmap_unlock() is passed a pointer that may be beyond the mapped PTE page. The issue occurs when the PTE iteration loop completes without finding a KSM page. After the loop, 'ptep' has been incremented past the last PTE entry. On ARM32 LPAE with 512 PTEs per page (512 * 8 = 4096 bytes), this means ptep points to the next page, outside the kmap'd region. When pte_unmap_unlock(ptep, ptl) calls kunmap_local(ptep), it unmaps the wrong page address, leaving the original kmap slot still mapped. The next kmap_local then finds this slot unexpectedly occupied: WARNING: mm/highmem.c:622 kunmap_local_indexed (address mismatch) kernel BUG at mm/highmem.c:564 __kmap_local_pfn_prot (slot not empty) Fix this by passing start_ptep to pte_unmap_unlock(), which always points within the originally mapped PTE page. Reproducer: Run LTP ksm03 test on ARM32 with HIGHMEM enabled. The test triggers KSM merging followed by unmerging (writing 0 then 2 to /sys/kernel/mm/ksm/run), which exercises break_ksm_pmd_entry(). Link: https://lkml.kernel.org/r/20251220202926.318366-1-sashal@kernel.org Fixes: 5d4939fc2258 ("ksm: perform a range-walk in break_ksm") Signed-off-by: Sasha Levin Assisted-by: claude-opus-4-5-20251101 Acked-by: David Hildenbrand (Red Hat) Reviewed-by: Chengming Zhou Cc: Pedro Demarchi Gomes Cc: xu xin Signed-off-by: Andrew Morton

mm: eliminate further swapops predicates

2025-11-24T23:08:52+00:00

Having converted so much of the code base to software leaf entries, we can mop up some remaining cases. We replace is_pfn_swap_entry(), pfn_swap_entry_to_page(), is_writable_device_private_entry(), is_device_exclusive_entry(), is_migration_entry(), is_writable_migration_entry(), is_readable_migration_entry(), swp_offset_pfn() and pfn_swap_entry_folio() with softleaf equivalents. No functional change intended. Link: https://lkml.kernel.org/r/956bc9c031604811c0070d2f4bf2f1373f230213.1762812360.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes Cc: Alexander Gordeev Cc: Alistair Popple Cc: Al Viro Cc: Arnd Bergmann Cc: Axel Rasmussen Cc: Baolin Wang Cc: Baoquan He Cc: Barry Song Cc: Byungchul Park Cc: Chengming Zhou Cc: Chris Li Cc: Christian Borntraeger Cc: Christian Brauner Cc: Claudio Imbrenda Cc: David Hildenbrand Cc: Dev Jain Cc: Gerald Schaefer Cc: Gregory Price Cc: Heiko Carstens Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Jann Horn Cc: Janosch Frank Cc: Jason Gunthorpe Cc: Joshua Hahn Cc: Kairui Song Cc: Kemeng Shi Cc: Lance Yang Cc: Leon Romanovsky Cc: Liam Howlett Cc: Mathew Brost Cc: Matthew Wilcox (Oracle) Cc: Miaohe Lin Cc: Michal Hocko Cc: Mike Rapoport Cc: Muchun Song Cc: Naoya Horiguchi Cc: Nhat Pham Cc: Nico Pache Cc: Oscar Salvador Cc: Pasha Tatashin Cc: Peter Xu Cc: Rakie Kim Cc: Rik van Riel Cc: Ryan Roberts Cc: SeongJae Park Cc: Suren Baghdasaryan Cc: Sven Schnelle Cc: Vasily Gorbik Cc: Vlastimil Babka Cc: Wei Xu Cc: xu xin Cc: Yuanchu Xie Cc: Zi Yan Signed-off-by: Andrew Morton

ksm: replace function unmerge_ksm_pages with break_ksm

2025-11-17T01:28:28+00:00

Function unmerge_ksm_pages() is unnecessary since now break_ksm() walks an address range. So replace it with break_ksm(). Link: https://lkml.kernel.org/r/20251105184912.186329-4-pedrodemargomes@gmail.com Signed-off-by: Pedro Demarchi Gomes Suggested-by: David Hildenbrand (Red Hat) Acked-by: David Hildenbrand (Red Hat) Signed-off-by: Andrew Morton

ksm: perform a range-walk in break_ksm

2025-11-17T01:28:28+00:00

Make break_ksm() receive an address range and change break_ksm_pmd_entry() to perform a range-walk and return the address of the first ksm page found. This change allows break_ksm() to skip unmapped regions instead of iterating every page address. When unmerging large sparse VMAs, this significantly reduces runtime. In a benchmark unmerging a 32 TiB sparse virtual address space where only one page was populated, the runtime dropped from 9 minutes to less then 5 seconds. Link: https://lkml.kernel.org/r/20251105184912.186329-3-pedrodemargomes@gmail.com Signed-off-by: Pedro Demarchi Gomes Suggested-by: David Hildenbrand (Red Hat) Acked-by: David Hildenbrand (Red Hat) Signed-off-by: Andrew Morton

Revert "mm/ksm: convert break_ksm() from walk_page_range_vma() to folio_walk"

2025-11-17T01:28:28+00:00

Patch series "ksm: perform a range-walk to jump over holes in break_ksm", v4. When unmerging an address range, unmerge_ksm_pages function walks every page address in the specified range to locate ksm pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions, causing the process to get blocked for several minutes. This patch makes break_ksm, function called by unmerge_ksm_pages for every page in an address range, perform a range walk, allowing it to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. As pointed out by David Hildenbrand in [1], unmerge_ksm_pages() is called from: * ksm_madvise() through madvise(MADV_UNMERGEABLE). There are not a lot of users of that function. * __ksm_del_vma() through ksm_del_vmas(). Effectively called when disabling KSM for a process either through the sysctl or from s390x gmap code when enabling storage keys for a VM. Consider the following test program which creates a 32 TiB mapping in the virtual address space but only populates a single page: #include #include #include /* 32 TiB */ const size_t size = 32ul * 1024 * 1024 * 1024 * 1024; int main() { char *area = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0); if (area == MAP_FAILED) { perror("mmap() failed\n"); return -1; } /* Populate a single page such that we get an anon_vma. */ *area = 0; /* Enable KSM. */ madvise(area, size, MADV_MERGEABLE); madvise(area, size, MADV_UNMERGEABLE); return 0; } Without this patch, this program takes 9 minutes to finish, while with this patch it finishes in less then 5 seconds. This patch (of 3): This reverts commit e317a8d8b4f600fc7ec9725e26417030ee594f52 and changes function break_ksm_pmd_entry() to use folios. This reverts break_ksm() to use walk_page_range_vma() instead of folio_walk_start(). Change break_ksm_pmd_entry() to call is_ksm_zero_pte() only if we know the folio is present, and also rename variable ret to found. This will make it easier to later modify break_ksm() to perform a proper range walk. Link: https://lkml.kernel.org/r/20251105184912.186329-1-pedrodemargomes@gmail.com Link: https://lkml.kernel.org/r/20251105184912.186329-2-pedrodemargomes@gmail.com Link: https://lore.kernel.org/linux-mm/e0886fdf-d198-4130-bd9a-be276c59da37@redhat.com/ [1] Signed-off-by: Pedro Demarchi Gomes Suggested-by: David Hildenbrand (Red Hat) Acked-by: David Hildenbrand (Red Hat) Signed-off-by: Andrew Morton

mm/ksm: fix exec/fork inheritance support for prctl

2025-11-17T01:27:55+00:00

Patch series "ksm: fix exec/fork inheritance", v2. This series fixes exec/fork inheritance. See the detailed description of the issue below. This patch (of 2): Background ========== commit d7597f59d1d33 ("mm: add new api to enable ksm per process") introduced MMF_VM_MERGE_ANY for mm->flags, and allowed user to set it by prctl() so that the process's VMAs are forcibly scanned by ksmd. Subsequently, the 3c6f33b7273a ("mm/ksm: support fork/exec for prctl") supported inheriting the MMF_VM_MERGE_ANY flag when a task calls execve(). Finally, commit 3a9e567ca45fb ("mm/ksm: fix ksm exec support for prctl") fixed the issue that ksmd doesn't scan the mm_struct with MMF_VM_MERGE_ANY by adding the mm_slot to ksm_mm_head in __bprm_mm_init(). Problem ======= In some extreme scenarios, however, this inheritance of MMF_VM_MERGE_ANY during exec/fork can fail. For example, when the scanning frequency of ksmd is tuned extremely high, a process carrying MMF_VM_MERGE_ANY may still fail to pass it to the newly exec'd process. This happens because ksm_execve() is executed too early in the do_execve flow (prematurely adding the new mm_struct to the ksm_mm_slot list). As a result, before do_execve completes, ksmd may have already performed a scan and found that this new mm_struct has no VM_MERGEABLE VMAs, thus clearing its MMF_VM_MERGE_ANY flag. Consequently, when the new program executes, the flag MMF_VM_MERGE_ANY inheritance missed. Root reason =========== commit d7597f59d1d33 ("mm: add new api to enable ksm per process") clear the flag MMF_VM_MERGE_ANY when ksmd found no VM_MERGEABLE VMAs. Solution ======== Firstly, Don't clear MMF_VM_MERGE_ANY when ksmd found no VM_MERGEABLE VMAs, because perhaps their mm_struct has just been added to ksm_mm_slot list, and its process has not yet officially started running or has not yet performed mmap/brk to allocate anonymous VMAS. Secondly, recheck MMF_VM_MERGEABLE again if a process takes MMF_VM_MERGE_ANY, and create a mm_slot and join it into ksm_scan_list again. Link: https://lkml.kernel.org/r/20251007182504440BJgK8VXRHh8TD7IGSUIY4@zte.com.cn Link: https://lkml.kernel.org/r/20251007182821572h_SoFqYZXEP1mvWI4n9VL@zte.com.cn Fixes: 3c6f33b7273a ("mm/ksm: support fork/exec for prctl") Fixes: d7597f59d1d3 ("mm: add new api to enable ksm per process") Signed-off-by: xu xin Cc: Stefan Roesch Cc: David Hildenbrand Cc: Jinjiang Tu Cc: Wang Yaxin Cc: Yang Yang Cc: Signed-off-by: Andrew Morton