Due to pmd sharing, the huge PTE pointer returned by huge_pte_alloc may not be valid. This can happen if a call to huge_pmd_unshare for the same pmd is made in another thread.
To address this issue, add a rw_semaphore (hinode_rwsem) to the hugetlbfs inode. - hinode_rwsem is taken in read mode before calling huge_pte_alloc, and held until finished with the returned pte pointer. - hinode_rwsem is held in write mode whenever huge_pmd_unshare is called. In the locking hierarchy, hinode_rwsem must be taken before a page lock. In an effort to minimize performance impacts, hinode_rwsem is not taken if the caller knows the target can not possibly be part of a shared pmd. lockdep_assert calls are added to huge_pmd_share and huge_pmd_unshare to help catch callers not using the proper locking. Signed-off-by: Mike Kravetz <[email protected]> --- fs/hugetlbfs/inode.c | 8 ++++ include/linux/hugetlb.h | 66 +++++++++++++++++++++++++++++-- mm/hugetlb.c | 86 +++++++++++++++++++++++++++++------------ mm/memory-failure.c | 15 ++++++- mm/migrate.c | 15 +++++++ mm/rmap.c | 3 +- mm/userfaultfd.c | 9 ++++- 7 files changed, 171 insertions(+), 31 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 3a1246aeedc4..d6bb675d4872 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -499,13 +499,17 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart, * Getting here in a truncate operation is a bug. */ if (unlikely(page_mapped(page))) { + struct hugetlbfs_inode_info *info = + HUGETLBFS_I(inode); BUG_ON(truncate_op); + down_write(&info->hinode_rwsem); i_mmap_lock_write(mapping); hugetlb_vmdelete_list(&mapping->i_mmap, index * pages_per_huge_page(h), (index + 1) * pages_per_huge_page(h)); i_mmap_unlock_write(mapping); + up_write(&info->hinode_rwsem); } lock_page(page); @@ -562,15 +566,18 @@ static int hugetlb_vmtruncate(struct inode *inode, loff_t offset) pgoff_t pgoff; struct address_space *mapping = inode->i_mapping; struct hstate *h = hstate_inode(inode); + struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode); BUG_ON(offset & ~huge_page_mask(h)); pgoff = offset >> PAGE_SHIFT; + down_write(&info->hinode_rwsem); i_size_write(inode, offset); i_mmap_lock_write(mapping); if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)) hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0); i_mmap_unlock_write(mapping); + up_write(&info->hinode_rwsem); remove_inode_hugepages(inode, offset, LLONG_MAX); return 0; } @@ -829,6 +836,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb, inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); inode->i_mapping->private_data = resv_map; info->seals = F_SEAL_SEAL; + init_rwsem(&info->hinode_rwsem); switch (mode & S_IFMT) { default: init_special_inode(inode, mode, dev); diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index bf79a5601091..10322fdcf3d9 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -163,7 +163,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz); pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz); -int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep); +int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long *addr, pte_t *ptep); void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end); struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address, @@ -196,8 +197,9 @@ static inline unsigned long hugetlb_total_pages(void) return 0; } -static inline int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, - pte_t *ptep) +static inline int huge_pmd_unshare(struct mm_struct *mm, + struct vm_area_struct *vma, + unsigned long *addr, pte_t *ptep) { return 0; } @@ -414,6 +416,7 @@ struct hugetlbfs_inode_info { struct shared_policy policy; struct inode vfs_inode; unsigned int seals; + struct rw_semaphore hinode_rwsem; }; static inline struct hugetlbfs_inode_info *HUGETLBFS_I(struct inode *inode) @@ -439,6 +442,51 @@ static inline struct hstate *hstate_inode(struct inode *i) { return HUGETLBFS_SB(i->i_sb)->hstate; } + +static inline bool vma_shareable(struct vm_area_struct *vma, unsigned long addr) +{ + unsigned long base = addr & PUD_MASK; + unsigned long end = base + PUD_SIZE; + + /* check on proper vm_flags and page table alignment */ + if (vma->vm_flags & VM_MAYSHARE && range_in_vma(vma, base, end)) + return true; + return false; +} + +static inline void hinode_lock_read(struct address_space *mapping, + struct vm_area_struct *vma, + unsigned long addr) +{ + if (!mapping) + return; + if (vma && !vma_shareable(vma, addr)) + return; + + down_read(&HUGETLBFS_I(mapping->host)->hinode_rwsem); +} + +static inline void hinode_unlock_read(struct address_space *mapping, + struct vm_area_struct *vma, + unsigned long addr) +{ + if (!mapping) + return; + if (vma && !vma_shareable(vma, addr)) + return; + + up_read(&HUGETLBFS_I(mapping->host)->hinode_rwsem); +} + +static inline void hinode_assert_locked(struct address_space *mapping) +{ + lockdep_assert_held(&HUGETLBFS_I(mapping->host)->hinode_rwsem); +} + +static inline void hinode_assert_write_locked(struct address_space *mapping) +{ + lockdep_assert_held_write(&HUGETLBFS_I(mapping->host)->hinode_rwsem); +} #else /* !CONFIG_HUGETLBFS */ #define is_file_hugepages(file) false @@ -913,6 +961,18 @@ static inline void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr pte_t *ptep, pte_t pte, unsigned long sz) { } + +static inline void hinode_lock_read(struct address_space *mapping, + struct vm_area_struct *vma, + unsigned long addr) +{ +} + +static inline void hinode_unlock_read(struct address_space *mapping, + struct vm_area_struct *vma, + unsigned long addr) +{ +} #endif /* CONFIG_HUGETLB_PAGE */ static inline spinlock_t *huge_pte_lock(struct hstate *h, diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9a316b6d0b51..940c037418f8 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3728,6 +3728,18 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, vma->vm_start, vma->vm_end); mmu_notifier_invalidate_range_start(&range); + } else { + /* + * For shared mappings hinode_rwsem must be held to call + * huge_pte_alloc, otherwise the returned ptep could go + * away if part of a shared pmd and another thread calls + * huge_pmd_unshare. + * + * Note: As an optimization We could check at each PUD_SIZE + * boundary to see if sharing is possible before taking + * hinode_rwsem. + */ + hinode_lock_read(vma->vm_file->f_mapping, NULL, 0UL); } for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) { @@ -3805,6 +3817,8 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, if (cow) mmu_notifier_invalidate_range_end(&range); + else + hinode_unlock_read(vma->vm_file->f_mapping, NULL, 0UL); return ret; } @@ -3848,7 +3862,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, continue; ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, &address, ptep)) { + if (huge_pmd_unshare(mm, vma, &address, ptep)) { spin_unlock(ptl); /* * We just unmapped a page of PMDs by clearing a PUD. @@ -4253,13 +4267,17 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm, }; /* - * hugetlb_fault_mutex must be dropped before - * handling userfault. Reacquire after handling + * hugetlb_fault_mutex and inode mutex must be dropped + * before handling userfault. Reacquire after handling * fault to make calling code simpler. */ hash = hugetlb_fault_mutex_hash(mapping, idx); mutex_unlock(&hugetlb_fault_mutex_table[hash]); + hinode_unlock_read(mapping, vma, address); + ret = handle_userfault(&vmf, VM_UFFD_MISSING); + + hinode_lock_read(mapping, vma, address); mutex_lock(&hugetlb_fault_mutex_table[hash]); goto out; } @@ -4424,6 +4442,11 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, ptep = huge_pte_offset(mm, haddr, huge_page_size(h)); if (ptep) { + /* + * Since we hold no locks, ptep could be stale. That is + * OK as we are only making decisions based on content and + * not actually modifying content here. + */ entry = huge_ptep_get(ptep); if (unlikely(is_hugetlb_entry_migration(entry))) { migration_entry_wait_huge(vma, mm, ptep); @@ -4431,20 +4454,32 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) return VM_FAULT_HWPOISON_LARGE | VM_FAULT_SET_HINDEX(hstate_index(h)); - } else { - ptep = huge_pte_alloc(mm, haddr, huge_page_size(h)); - if (!ptep) - return VM_FAULT_OOM; } + /* + * Acquire hinode_sema before calling huge_pte_alloc and hold + * until finished with ptep. This prevents huge_pmd_unshare from + * being called elsewhere and making the ptep no longer valid. + * + * ptep could have already be assigned via huge_pte_offset. That + * is OK, as huge_pte_alloc will return the same value unless + * something has changed. + */ mapping = vma->vm_file->f_mapping; - idx = vma_hugecache_offset(h, vma, haddr); + hinode_lock_read(mapping, vma, address); + ptep = huge_pte_alloc(mm, haddr, huge_page_size(h)); + if (!ptep) { + ret = VM_FAULT_OOM; + goto out_mutex; + } + /* * Serialize hugepage allocation and instantiation, so that we don't * get spurious allocation failures if two CPUs race to instantiate * the same page in the page cache. */ + idx = vma_hugecache_offset(h, vma, haddr); hash = hugetlb_fault_mutex_hash(mapping, idx); mutex_lock(&hugetlb_fault_mutex_table[hash]); @@ -4532,6 +4567,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } out_mutex: mutex_unlock(&hugetlb_fault_mutex_table[hash]); + hinode_unlock_read(mapping, vma, address); /* * Generally it's safe to hold refcount during waiting page lock. But * here we just wait to defer the next page fault to avoid busy loop and @@ -4872,6 +4908,8 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, unsigned long pages = 0; bool shared_pmd = false; struct mmu_notifier_range range; + struct hugetlbfs_inode_info *hinfo = + HUGETLBFS_I(vma->vm_file->f_inode); /* * In the case of shared PMDs, the area to flush could be beyond @@ -4886,6 +4924,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, flush_cache_range(vma, range.start, range.end); mmu_notifier_invalidate_range_start(&range); + down_write(&hinfo->hinode_rwsem); i_mmap_lock_write(vma->vm_file->f_mapping); for (; address < end; address += huge_page_size(h)) { spinlock_t *ptl; @@ -4893,7 +4932,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, if (!ptep) continue; ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, &address, ptep)) { + if (huge_pmd_unshare(mm, vma, &address, ptep)) { pages++; spin_unlock(ptl); shared_pmd = true; @@ -4948,6 +4987,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma, * See Documentation/vm/mmu_notifier.rst */ i_mmap_unlock_write(vma->vm_file->f_mapping); + up_write(&hinfo->hinode_rwsem); mmu_notifier_invalidate_range_end(&range); return pages << h->order; @@ -5166,19 +5206,6 @@ static unsigned long page_table_shareable(struct vm_area_struct *svma, return saddr; } -static bool vma_shareable(struct vm_area_struct *vma, unsigned long addr) -{ - unsigned long base = addr & PUD_MASK; - unsigned long end = base + PUD_SIZE; - - /* - * check on proper vm_flags and page table alignment - */ - if (vma->vm_flags & VM_MAYSHARE && range_in_vma(vma, base, end)) - return true; - return false; -} - /* * Determine if start,end range within vma could be mapped by shared pmd. * If yes, adjust start and end to cover range associated with possible @@ -5212,6 +5239,10 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, * pud has to be populated inside the same i_mmap_rwsem section - otherwise * racing tasks could either miss the sharing (see huge_pte_offset) or select a * bad pmd for sharing. + * + * This should be called with hinode_rwsem held in read mode. Otherwise, it + * could race with huge_pmd_unshare and the pte_t pointer could become invalid + * before being returned to the caller. */ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) { @@ -5227,6 +5258,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) if (!vma_shareable(vma, addr)) return (pte_t *)pmd_alloc(mm, pud, addr); + hinode_assert_locked(mapping); i_mmap_lock_read(mapping); vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) { @@ -5269,12 +5301,13 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) * indicated by page_count > 1, unmap is achieved by clearing pud and * decrementing the ref count. If count == 1, the pte page is not shared. * - * called with page table lock held. + * Called with page table lock held and hinode_rwsem held in write mode. * * returns: 1 successfully unmapped a shared pte page * 0 the underlying pte page is not shared, or it is the last user */ -int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep) +int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long *addr, pte_t *ptep) { pgd_t *pgd = pgd_offset(mm, *addr); p4d_t *p4d = p4d_offset(pgd, *addr); @@ -5284,6 +5317,8 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep) if (page_count(virt_to_page(ptep)) == 1) return 0; + hinode_assert_write_locked(vma->vm_file->f_mapping); + pud_clear(pud); put_page(virt_to_page(ptep)); mm_dec_nr_pmds(mm); @@ -5297,7 +5332,8 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) return NULL; } -int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep) +int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, + unsigned long *addr, pte_t *ptep) { return 0; } diff --git a/mm/memory-failure.c b/mm/memory-failure.c index 0c4f8cbc772e..fd6ee4d941a0 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1054,7 +1054,20 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn, if (kill) collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED); - unmap_success = try_to_unmap(hpage, ttu); + if (PageHuge(hpage) && !PageAnon(hpage) && mapping) { + struct hugetlbfs_inode_info *hinode_info = + HUGETLBFS_I(mapping->host); + /* + * For hugetlb pages, try_to_unmap could potentially call + * huge_pmd_unshare. Because of this, take hinode_rwsem + * in write mode before calling. + */ + down_write(&hinode_info->hinode_rwsem); + unmap_success = try_to_unmap(hpage, ttu); + up_write(&hinode_info->hinode_rwsem); + } else { + unmap_success = try_to_unmap(hpage, ttu); + } if (!unmap_success) pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n", pfn, page_mapcount(hpage)); diff --git a/mm/migrate.c b/mm/migrate.c index 05c3c2e569df..f068727293c2 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1327,9 +1327,24 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, goto put_anon; if (page_mapped(hpage)) { + struct address_space *mapping = NULL; + struct hugetlbfs_inode_info *hinode_info; + /* + * try_to_unmap could potentially call huge_pmd_unshare. + * Take hinode_rwsem if sharing is possible. + */ + if (!PageAnon(hpage)) { + mapping = page_mapping(hpage); + if (mapping) { + hinode_info = HUGETLBFS_I(mapping->host); + down_write(&hinode_info->hinode_rwsem); + } + } try_to_unmap(hpage, TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS); page_was_mapped = 1; + if (mapping) + up_write(&hinode_info->hinode_rwsem); } if (!page_mapped(hpage)) diff --git a/mm/rmap.c b/mm/rmap.c index 8ef12940e357..9e65c9c95449 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -22,6 +22,7 @@ * * inode->i_mutex (while writing or truncating, not reading or faulting) * mm->mmap_lock + * hugetlbfs inode->hinode_rwsem (hugetlbfs specific) * page->flags PG_locked (lock_page) * hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share) * mapping->i_mmap_rwsem @@ -1455,7 +1456,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma, address = pvmw.address; if (PageHuge(page)) { - if (huge_pmd_unshare(mm, &address, pvmw.pte)) { + if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) { /* * huge_pmd_unshare unmapped an entire PMD * page. There is no way of knowing exactly diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index ab9e0496d601..3ca789934f6f 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -278,10 +278,14 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, BUG_ON(dst_addr >= dst_start + len); /* - * Serialize via hugetlb_fault_mutex + * Serialize via hinode_rwsem hugetlb_fault_mutex. + * hinode_rwsem ensures the dst_pte remains valid even + * in the case of shared pmds. fault mutex prevents + * races with other faulting threads. */ idx = linear_page_index(dst_vma, dst_addr); mapping = dst_vma->vm_file->f_mapping; + hinode_lock_read(mapping, dst_vma, dst_addr); hash = hugetlb_fault_mutex_hash(mapping, idx); mutex_lock(&hugetlb_fault_mutex_table[hash]); @@ -289,6 +293,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, dst_pte = huge_pte_alloc(dst_mm, dst_addr, vma_hpagesize); if (!dst_pte) { mutex_unlock(&hugetlb_fault_mutex_table[hash]); + hinode_unlock_read(mapping, dst_vma, dst_addr); goto out_unlock; } @@ -296,6 +301,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, dst_pteval = huge_ptep_get(dst_pte); if (!huge_pte_none(dst_pteval)) { mutex_unlock(&hugetlb_fault_mutex_table[hash]); + hinode_unlock_read(mapping, dst_vma, dst_addr); goto out_unlock; } @@ -303,6 +309,7 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm, dst_addr, src_addr, &page); mutex_unlock(&hugetlb_fault_mutex_table[hash]); + hinode_unlock_read(mapping, dst_vma, dst_addr); vm_alloc_shared = vm_shared; cond_resched(); -- 2.25.4
