The patch titled Subject: hugetlbfs: close race between MADV_DONTNEED and page fault has been added to the -mm mm-hotfixes-unstable branch. Its filename is hugetlbfs-close-race-between-madv_dontneed-and-page-fault.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Rik van Riel riel@surriel.com Subject: hugetlbfs: close race between MADV_DONTNEED and page fault Date: Thu, 5 Oct 2023 23:59:08 -0400

Malloc libraries, like jemalloc and tcalloc, take decisions on when to call madvise independently from the code in the main application.

This sometimes results in the application page faulting on an address, right after the malloc library has shot down the backing memory with MADV_DONTNEED.

Usually this is harmless, because we always have some 4kB pages sitting around to satisfy a page fault. However, with hugetlbfs systems often allocate only the exact number of huge pages that the application wants.

Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of any lock taken on the page fault path, which can open up the following race condition:

CPU 1 CPU 2

MADV_DONTNEED unmap page shoot down TLB entry page fault fail to allocate a huge page killed with SIGBUS free page

Fix that race by pulling the locking from __unmap_hugepage_final_range into helper functions called from zap_page_range_single. This ensures page faults stay locked out of the MADV_DONTNEED VMA until the huge pages have actually been freed.

Link: https://lkml.kernel.org/r/20231006040020.3677377-4-riel@surriel.com Fixes: 04ada095dcfc ("hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing") Signed-off-by: Rik van Riel riel@surriel.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Muchun Song muchun.song@linux.dev Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/hugetlb.h | 35 +++++++++++++++++++++++++++++++++-- mm/hugetlb.c | 34 ++++++++++++++++++++++------------ mm/memory.c | 13 ++++++++----- 3 files changed, 63 insertions(+), 19 deletions(-)

--- a/include/linux/hugetlb.h~hugetlbfs-close-race-between-madv_dontneed-and-page-fault +++ a/include/linux/hugetlb.h @@ -139,7 +139,7 @@ struct page *hugetlb_follow_page_mask(st void unmap_hugepage_range(struct vm_area_struct *, unsigned long, unsigned long, struct page *, zap_flags_t); -void __unmap_hugepage_range_final(struct mmu_gather *tlb, +void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long start, unsigned long end, struct page *ref_page, zap_flags_t zap_flags); @@ -246,6 +246,25 @@ int huge_pmd_unshare(struct mm_struct *m void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end);

+extern void __hugetlb_zap_begin(struct vm_area_struct *vma, + unsigned long *begin, unsigned long *end); +extern void __hugetlb_zap_end(struct vm_area_struct *vma, + struct zap_details *details); + +static inline void hugetlb_zap_begin(struct vm_area_struct *vma, + unsigned long *start, unsigned long *end) +{ + if (is_vm_hugetlb_page(vma)) + __hugetlb_zap_begin(vma, start, end); +} + +static inline void hugetlb_zap_end(struct vm_area_struct *vma, + struct zap_details *details) +{ + if (is_vm_hugetlb_page(vma)) + __hugetlb_zap_end(vma, details); +} + void hugetlb_vma_lock_read(struct vm_area_struct *vma); void hugetlb_vma_unlock_read(struct vm_area_struct *vma); void hugetlb_vma_lock_write(struct vm_area_struct *vma); @@ -297,6 +316,18 @@ static inline void adjust_range_if_pmd_s { }

+static inline void hugetlb_zap_begin( + struct vm_area_struct *vma, + unsigned long *start, unsigned long *end) +{ +} + +static inline void hugetlb_zap_end( + struct vm_area_struct *vma, + struct zap_details *details) +{ +} + static inline struct page *hugetlb_follow_page_mask( struct vm_area_struct *vma, unsigned long address, unsigned int flags, unsigned int *page_mask) @@ -442,7 +473,7 @@ static inline long hugetlb_change_protec return 0; }

-static inline void __unmap_hugepage_range_final(struct mmu_gather *tlb, +static inline void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long start, unsigned long end, struct page *ref_page, zap_flags_t zap_flags) --- a/mm/hugetlb.c~hugetlbfs-close-race-between-madv_dontneed-and-page-fault +++ a/mm/hugetlb.c @@ -5306,9 +5306,9 @@ int move_hugetlb_page_tables(struct vm_a return len + old_addr - old_end; }

-static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, - unsigned long start, unsigned long end, - struct page *ref_page, zap_flags_t zap_flags) +void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, + unsigned long start, unsigned long end, + struct page *ref_page, zap_flags_t zap_flags) { struct mm_struct *mm = vma->vm_mm; unsigned long address; @@ -5437,16 +5437,25 @@ static void __unmap_hugepage_range(struc tlb_flush_mmu_tlbonly(tlb); }

-void __unmap_hugepage_range_final(struct mmu_gather *tlb, - struct vm_area_struct *vma, unsigned long start, - unsigned long end, struct page *ref_page, - zap_flags_t zap_flags) +void __hugetlb_zap_begin(struct vm_area_struct *vma, + unsigned long *start, unsigned long *end) { + if (!vma->vm_file) /* hugetlbfs_file_mmap error */ + return; + + adjust_range_if_pmd_sharing_possible(vma, start, end); hugetlb_vma_lock_write(vma); - i_mmap_lock_write(vma->vm_file->f_mapping); + if (vma->vm_file) + i_mmap_lock_write(vma->vm_file->f_mapping); +} + +void __hugetlb_zap_end(struct vm_area_struct *vma, + struct zap_details *details) +{ + zap_flags_t zap_flags = details ? details->zap_flags : 0;

- /* mmu notification performed in caller */ - __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags); + if (!vma->vm_file) /* hugetlbfs_file_mmap error */ + return;

if (zap_flags & ZAP_FLAG_UNMAP) { /* final unmap */ /* @@ -5459,11 +5468,12 @@ void __unmap_hugepage_range_final(struct * someone else. */ __hugetlb_vma_unlock_write_free(vma); - i_mmap_unlock_write(vma->vm_file->f_mapping); } else { - i_mmap_unlock_write(vma->vm_file->f_mapping); hugetlb_vma_unlock_write(vma); } + + if (vma->vm_file) + i_mmap_unlock_write(vma->vm_file->f_mapping); }

void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, --- a/mm/memory.c~hugetlbfs-close-race-between-madv_dontneed-and-page-fault +++ a/mm/memory.c @@ -1683,7 +1683,7 @@ static void unmap_single_vma(struct mmu_ if (vma->vm_file) { zap_flags_t zap_flags = details ? details->zap_flags : 0; - __unmap_hugepage_range_final(tlb, vma, start, end, + __unmap_hugepage_range(tlb, vma, start, end, NULL, zap_flags); } } else @@ -1728,8 +1728,12 @@ void unmap_vmas(struct mmu_gather *tlb, start_addr, end_addr); mmu_notifier_invalidate_range_start(&range); do { - unmap_single_vma(tlb, vma, start_addr, end_addr, &details, + unsigned long start = start_addr; + unsigned long end = end_addr; + hugetlb_zap_begin(vma, &start, &end); + unmap_single_vma(tlb, vma, start, end, &details, mm_wr_locked); + hugetlb_zap_end(vma, &details); } while ((vma = mas_find(mas, tree_end - 1)) != NULL); mmu_notifier_invalidate_range_end(&range); } @@ -1753,9 +1757,7 @@ void zap_page_range_single(struct vm_are lru_add_drain(); mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm, address, end); - if (is_vm_hugetlb_page(vma)) - adjust_range_if_pmd_sharing_possible(vma, &range.start, - &range.end); + hugetlb_zap_begin(vma, &range.start, &range.end); tlb_gather_mmu(&tlb, vma->vm_mm); update_hiwater_rss(vma->vm_mm); mmu_notifier_invalidate_range_start(&range); @@ -1766,6 +1768,7 @@ void zap_page_range_single(struct vm_are unmap_single_vma(&tlb, vma, address, end, details, false); mmu_notifier_invalidate_range_end(&range); tlb_finish_mmu(&tlb); + hugetlb_zap_end(vma, details); }

/** _

Patches currently in -mm which might be from riel@surriel.com are

hugetlbfs-clear-resv_map-pointer-if-mmap-fails.patch hugetlbfs-extend-hugetlb_vma_lock-to-private-vmas.patch hugetlbfs-close-race-between-madv_dontneed-and-page-fault.patch