diff options
Diffstat (limited to 'mm/pagewalk.c')
| -rw-r--r-- | mm/pagewalk.c | 1030 |
1 files changed, 1030 insertions, 0 deletions
diff --git a/mm/pagewalk.c b/mm/pagewalk.c new file mode 100644 index 000000000..cc07fcf50 --- /dev/null +++ b/mm/pagewalk.c @@ -0,0 +1,1030 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/pagewalk.h> +#include <linux/highmem.h> +#include <linux/sched.h> +#include <linux/hugetlb.h> +#include <linux/mmu_context.h> +#include <linux/swap.h> + +#include <asm/tlbflush.h> + +#include "internal.h" + +/* + * We want to know the real level where a entry is located ignoring any + * folding of levels which may be happening. For example if p4d is folded then + * a missing entry found at level 1 (p4d) is actually at level 0 (pgd). + */ +static int real_depth(int depth) +{ + if (depth == 3 && PTRS_PER_PMD == 1) + depth = 2; + if (depth == 2 && PTRS_PER_PUD == 1) + depth = 1; + if (depth == 1 && PTRS_PER_P4D == 1) + depth = 0; + return depth; +} + +static int walk_pte_range_inner(pte_t *pte, unsigned long addr, + unsigned long end, struct mm_walk *walk) +{ + const struct mm_walk_ops *ops = walk->ops; + int err = 0; + + for (;;) { + if (ops->install_pte && pte_none(ptep_get(pte))) { + pte_t new_pte; + + err = ops->install_pte(addr, addr + PAGE_SIZE, &new_pte, + walk); + if (err) + break; + + set_pte_at(walk->mm, addr, pte, new_pte); + /* Non-present before, so for arches that need it. */ + if (!WARN_ON_ONCE(walk->no_vma)) + update_mmu_cache(walk->vma, addr, pte); + } else { + err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk); + if (err) + break; + } + if (addr >= end - PAGE_SIZE) + break; + addr += PAGE_SIZE; + pte++; + } + return err; +} + +static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + pte_t *pte; + int err = 0; + spinlock_t *ptl; + + if (walk->no_vma) { + /* + * pte_offset_map() might apply user-specific validation. + * Indeed, on x86_64 the pmd entries set up by init_espfix_ap() + * fit its pmd_bad() check (_PAGE_NX set and _PAGE_RW clear), + * and CONFIG_EFI_PGT_DUMP efi_mm goes so far as to walk them. + */ + if (walk->mm == &init_mm || addr >= TASK_SIZE) + pte = pte_offset_kernel(pmd, addr); + else + pte = pte_offset_map(pmd, addr); + if (pte) { + err = walk_pte_range_inner(pte, addr, end, walk); + if (walk->mm != &init_mm && addr < TASK_SIZE) + pte_unmap(pte); + } + } else { + pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl); + if (pte) { + err = walk_pte_range_inner(pte, addr, end, walk); + pte_unmap_unlock(pte, ptl); + } + } + if (!pte) + walk->action = ACTION_AGAIN; + return err; +} + +static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + pud_t pudval = pudp_get(pud); + pmd_t *pmd; + unsigned long next; + const struct mm_walk_ops *ops = walk->ops; + bool has_handler = ops->pte_entry; + bool has_install = ops->install_pte; + int err = 0; + int depth = real_depth(3); + + /* + * For PTE handling, pte_offset_map_lock() takes care of checking + * whether there actually is a page table. But it also has to be + * very careful about concurrent page table reclaim. + * + * Similarly, we have to be careful here - a PUD entry that points + * to a PMD table cannot go away, so we can just walk it. But if + * it's something else, we need to ensure we didn't race something, + * so need to retry. + * + * A pertinent example of this is a PUD refault after PUD split - + * we will need to split again or risk accessing invalid memory. + */ + if (!pud_present(pudval) || pud_leaf(pudval)) { + walk->action = ACTION_AGAIN; + return 0; + } + + pmd = pmd_offset(pud, addr); + do { +again: + walk->action = ACTION_SUBTREE; + next = pmd_addr_end(addr, end); + if (pmd_none(*pmd)) { + if (has_install) + err = __pte_alloc(walk->mm, pmd); + else if (ops->pte_hole) + err = ops->pte_hole(addr, next, depth, walk); + if (err) + break; + if (!has_install) + continue; + } + + /* + * This implies that each ->pmd_entry() handler + * needs to know about pmd_trans_huge() pmds + */ + if (ops->pmd_entry) + err = ops->pmd_entry(pmd, addr, next, walk); + if (err) + break; + + if (walk->action == ACTION_AGAIN) + goto again; + if (walk->action == ACTION_CONTINUE) + continue; + + if (!has_handler) { /* No handlers for lower page tables. */ + if (!has_install) + continue; /* Nothing to do. */ + /* + * We are ONLY installing, so avoid unnecessarily + * splitting a present huge page. + */ + if (pmd_present(*pmd) && pmd_trans_huge(*pmd)) + continue; + } + + if (walk->vma) + split_huge_pmd(walk->vma, pmd, addr); + else if (pmd_leaf(*pmd) || !pmd_present(*pmd)) + continue; /* Nothing to do. */ + + err = walk_pte_range(pmd, addr, next, walk); + if (err) + break; + + if (walk->action == ACTION_AGAIN) + goto again; + + } while (pmd++, addr = next, addr != end); + + return err; +} + +static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + pud_t *pud; + unsigned long next; + const struct mm_walk_ops *ops = walk->ops; + bool has_handler = ops->pmd_entry || ops->pte_entry; + bool has_install = ops->install_pte; + int err = 0; + int depth = real_depth(2); + + pud = pud_offset(p4d, addr); + do { + again: + walk->action = ACTION_SUBTREE; + next = pud_addr_end(addr, end); + if (pud_none(*pud)) { + if (has_install) + err = __pmd_alloc(walk->mm, pud, addr); + else if (ops->pte_hole) + err = ops->pte_hole(addr, next, depth, walk); + if (err) + break; + if (!has_install) + continue; + } + + if (ops->pud_entry) + err = ops->pud_entry(pud, addr, next, walk); + if (err) + break; + + if (walk->action == ACTION_AGAIN) + goto again; + if (walk->action == ACTION_CONTINUE) + continue; + + if (!has_handler) { /* No handlers for lower page tables. */ + if (!has_install) + continue; /* Nothing to do. */ + /* + * We are ONLY installing, so avoid unnecessarily + * splitting a present huge page. + */ + if (pud_present(*pud) && pud_trans_huge(*pud)) + continue; + } + + if (walk->vma) + split_huge_pud(walk->vma, pud, addr); + else if (pud_leaf(*pud) || !pud_present(*pud)) + continue; /* Nothing to do. */ + + err = walk_pmd_range(pud, addr, next, walk); + if (err) + break; + + if (walk->action == ACTION_AGAIN) + goto again; + } while (pud++, addr = next, addr != end); + + return err; +} + +static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + p4d_t *p4d; + unsigned long next; + const struct mm_walk_ops *ops = walk->ops; + bool has_handler = ops->pud_entry || ops->pmd_entry || ops->pte_entry; + bool has_install = ops->install_pte; + int err = 0; + int depth = real_depth(1); + + p4d = p4d_offset(pgd, addr); + do { + next = p4d_addr_end(addr, end); + if (p4d_none_or_clear_bad(p4d)) { + if (has_install) + err = __pud_alloc(walk->mm, p4d, addr); + else if (ops->pte_hole) + err = ops->pte_hole(addr, next, depth, walk); + if (err) + break; + if (!has_install) + continue; + } + if (ops->p4d_entry) { + err = ops->p4d_entry(p4d, addr, next, walk); + if (err) + break; + } + if (has_handler || has_install) + err = walk_pud_range(p4d, addr, next, walk); + if (err) + break; + } while (p4d++, addr = next, addr != end); + + return err; +} + +static int walk_pgd_range(unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + pgd_t *pgd; + unsigned long next; + const struct mm_walk_ops *ops = walk->ops; + bool has_handler = ops->p4d_entry || ops->pud_entry || ops->pmd_entry || + ops->pte_entry; + bool has_install = ops->install_pte; + int err = 0; + + if (walk->pgd) + pgd = walk->pgd + pgd_index(addr); + else + pgd = pgd_offset(walk->mm, addr); + do { + next = pgd_addr_end(addr, end); + if (pgd_none_or_clear_bad(pgd)) { + if (has_install) + err = __p4d_alloc(walk->mm, pgd, addr); + else if (ops->pte_hole) + err = ops->pte_hole(addr, next, 0, walk); + if (err) + break; + if (!has_install) + continue; + } + if (ops->pgd_entry) { + err = ops->pgd_entry(pgd, addr, next, walk); + if (err) + break; + } + if (has_handler || has_install) + err = walk_p4d_range(pgd, addr, next, walk); + if (err) + break; + } while (pgd++, addr = next, addr != end); + + return err; +} + +#ifdef CONFIG_HUGETLB_PAGE +static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr, + unsigned long end) +{ + unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h); + + return min(boundary, end); +} + +static int walk_hugetlb_range(unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + struct vm_area_struct *vma = walk->vma; + struct hstate *h = hstate_vma(vma); + unsigned long next; + unsigned long hmask = huge_page_mask(h); + unsigned long sz = huge_page_size(h); + pte_t *pte; + const struct mm_walk_ops *ops = walk->ops; + int err = 0; + + hugetlb_vma_lock_read(vma); + do { + next = hugetlb_entry_end(h, addr, end); + pte = hugetlb_walk(vma, addr & hmask, sz); + if (pte) + err = ops->hugetlb_entry(pte, hmask, addr, next, walk); + else if (ops->pte_hole) + err = ops->pte_hole(addr, next, -1, walk); + if (err) + break; + } while (addr = next, addr != end); + hugetlb_vma_unlock_read(vma); + + return err; +} + +#else /* CONFIG_HUGETLB_PAGE */ +static int walk_hugetlb_range(unsigned long addr, unsigned long end, + struct mm_walk *walk) +{ + return 0; +} + +#endif /* CONFIG_HUGETLB_PAGE */ + +/* + * Decide whether we really walk over the current vma on [@start, @end) + * or skip it via the returned value. Return 0 if we do walk over the + * current vma, and return 1 if we skip the vma. Negative values means + * error, where we abort the current walk. + */ +static int walk_page_test(unsigned long start, unsigned long end, + struct mm_walk *walk) +{ + struct vm_area_struct *vma = walk->vma; + const struct mm_walk_ops *ops = walk->ops; + + if (ops->test_walk) + return ops->test_walk(start, end, walk); + + /* + * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP + * range, so we don't walk over it as we do for normal vmas. However, + * Some callers are interested in handling hole range and they don't + * want to just ignore any single address range. Such users certainly + * define their ->pte_hole() callbacks, so let's delegate them to handle + * vma(VM_PFNMAP). + */ + if (vma->vm_flags & VM_PFNMAP) { + int err = 1; + if (ops->pte_hole) + err = ops->pte_hole(start, end, -1, walk); + return err ? err : 1; + } + return 0; +} + +static int __walk_page_range(unsigned long start, unsigned long end, + struct mm_walk *walk) +{ + int err = 0; + struct vm_area_struct *vma = walk->vma; + const struct mm_walk_ops *ops = walk->ops; + bool is_hugetlb = is_vm_hugetlb_page(vma); + + /* We do not support hugetlb PTE installation. */ + if (ops->install_pte && is_hugetlb) + return -EINVAL; + + if (ops->pre_vma) { + err = ops->pre_vma(start, end, walk); + if (err) + return err; + } + + if (is_hugetlb) { + if (ops->hugetlb_entry) + err = walk_hugetlb_range(start, end, walk); + } else + err = walk_pgd_range(start, end, walk); + + if (ops->post_vma) + ops->post_vma(walk); + + return err; +} + +static inline void process_mm_walk_lock(struct mm_struct *mm, + enum page_walk_lock walk_lock) +{ + if (walk_lock == PGWALK_RDLOCK) + mmap_assert_locked(mm); + else if (walk_lock != PGWALK_VMA_RDLOCK_VERIFY) + mmap_assert_write_locked(mm); +} + +static inline void process_vma_walk_lock(struct vm_area_struct *vma, + enum page_walk_lock walk_lock) +{ +#ifdef CONFIG_PER_VMA_LOCK + switch (walk_lock) { + case PGWALK_WRLOCK: + vma_start_write(vma); + break; + case PGWALK_WRLOCK_VERIFY: + vma_assert_write_locked(vma); + break; + case PGWALK_VMA_RDLOCK_VERIFY: + vma_assert_locked(vma); + break; + case PGWALK_RDLOCK: + /* PGWALK_RDLOCK is handled by process_mm_walk_lock */ + break; + } +#endif +} + +/* + * See the comment for walk_page_range(), this performs the heavy lifting of the + * operation, only sets no restrictions on how the walk proceeds. + * + * We usually restrict the ability to install PTEs, but this functionality is + * available to internal memory management code and provided in mm/internal.h. + */ +int walk_page_range_mm_unsafe(struct mm_struct *mm, unsigned long start, + unsigned long end, const struct mm_walk_ops *ops, + void *private) +{ + int err = 0; + unsigned long next; + struct vm_area_struct *vma; + struct mm_walk walk = { + .ops = ops, + .mm = mm, + .private = private, + }; + + if (start >= end) + return -EINVAL; + + if (!walk.mm) + return -EINVAL; + + process_mm_walk_lock(walk.mm, ops->walk_lock); + + vma = find_vma(walk.mm, start); + do { + if (!vma) { /* after the last vma */ + walk.vma = NULL; + next = end; + if (ops->pte_hole) + err = ops->pte_hole(start, next, -1, &walk); + } else if (start < vma->vm_start) { /* outside vma */ + walk.vma = NULL; + next = min(end, vma->vm_start); + if (ops->pte_hole) + err = ops->pte_hole(start, next, -1, &walk); + } else { /* inside vma */ + process_vma_walk_lock(vma, ops->walk_lock); + walk.vma = vma; + next = min(end, vma->vm_end); + vma = find_vma(mm, vma->vm_end); + + err = walk_page_test(start, next, &walk); + if (err > 0) { + /* + * positive return values are purely for + * controlling the pagewalk, so should never + * be passed to the callers. + */ + err = 0; + continue; + } + if (err < 0) + break; + err = __walk_page_range(start, next, &walk); + } + if (err) + break; + } while (start = next, start < end); + return err; +} + +/* + * Determine if the walk operations specified are permitted to be used for a + * page table walk. + * + * This check is performed on all functions which are parameterised by walk + * operations and exposed in include/linux/pagewalk.h. + * + * Internal memory management code can use *_unsafe() functions to be able to + * use all page walking operations. + */ +static bool check_ops_safe(const struct mm_walk_ops *ops) +{ + /* + * The installation of PTEs is solely under the control of memory + * management logic and subject to many subtle locking, security and + * cache considerations so we cannot permit other users to do so, and + * certainly not for exported symbols. + */ + if (ops->install_pte) + return false; + + return true; +} + +/** + * walk_page_range - walk page table with caller specific callbacks + * @mm: mm_struct representing the target process of page table walk + * @start: start address of the virtual address range + * @end: end address of the virtual address range + * @ops: operation to call during the walk + * @private: private data for callbacks' usage + * + * Recursively walk the page table tree of the process represented by @mm + * within the virtual address range [@start, @end). During walking, we can do + * some caller-specific works for each entry, by setting up pmd_entry(), + * pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these + * callbacks, the associated entries/pages are just ignored. + * The return values of these callbacks are commonly defined like below: + * + * - 0 : succeeded to handle the current entry, and if you don't reach the + * end address yet, continue to walk. + * - >0 : succeeded to handle the current entry, and return to the caller + * with caller specific value. + * - <0 : failed to handle the current entry, and return to the caller + * with error code. + * + * Before starting to walk page table, some callers want to check whether + * they really want to walk over the current vma, typically by checking + * its vm_flags. walk_page_test() and @ops->test_walk() are used for this + * purpose. + * + * If operations need to be staged before and committed after a vma is walked, + * there are two callbacks, pre_vma() and post_vma(). Note that post_vma(), + * since it is intended to handle commit-type operations, can't return any + * errors. + * + * struct mm_walk keeps current values of some common data like vma and pmd, + * which are useful for the access from callbacks. If you want to pass some + * caller-specific data to callbacks, @private should be helpful. + * + * Locking: + * Callers of walk_page_range() and walk_page_vma() should hold @mm->mmap_lock, + * because these function traverse vma list and/or access to vma's data. + */ +int walk_page_range(struct mm_struct *mm, unsigned long start, + unsigned long end, const struct mm_walk_ops *ops, + void *private) +{ + if (!check_ops_safe(ops)) + return -EINVAL; + + return walk_page_range_mm_unsafe(mm, start, end, ops, private); +} + +/** + * walk_kernel_page_table_range - walk a range of kernel pagetables. + * @start: start address of the virtual address range + * @end: end address of the virtual address range + * @ops: operation to call during the walk + * @pgd: pgd to walk if different from mm->pgd + * @private: private data for callbacks' usage + * + * Similar to walk_page_range() but can walk any page tables even if they are + * not backed by VMAs. Because 'unusual' entries may be walked this function + * will also not lock the PTEs for the pte_entry() callback. This is useful for + * walking kernel pages tables or page tables for firmware. + * + * Note: Be careful to walk the kernel pages tables, the caller may be need to + * take other effective approaches (mmap lock may be insufficient) to prevent + * the intermediate kernel page tables belonging to the specified address range + * from being freed (e.g. memory hot-remove). + */ +int walk_kernel_page_table_range(unsigned long start, unsigned long end, + const struct mm_walk_ops *ops, pgd_t *pgd, void *private) +{ + /* + * Kernel intermediate page tables are usually not freed, so the mmap + * read lock is sufficient. But there are some exceptions. + * E.g. memory hot-remove. In which case, the mmap lock is insufficient + * to prevent the intermediate kernel pages tables belonging to the + * specified address range from being freed. The caller should take + * other actions to prevent this race. + */ + mmap_assert_locked(&init_mm); + + return walk_kernel_page_table_range_lockless(start, end, ops, pgd, + private); +} + +/* + * Use this function to walk the kernel page tables locklessly. It should be + * guaranteed that the caller has exclusive access over the range they are + * operating on - that there should be no concurrent access, for example, + * changing permissions for vmalloc objects. + */ +int walk_kernel_page_table_range_lockless(unsigned long start, unsigned long end, + const struct mm_walk_ops *ops, pgd_t *pgd, void *private) +{ + struct mm_walk walk = { + .ops = ops, + .mm = &init_mm, + .pgd = pgd, + .private = private, + .no_vma = true + }; + + if (start >= end) + return -EINVAL; + if (!check_ops_safe(ops)) + return -EINVAL; + + return walk_pgd_range(start, end, &walk); +} + +/** + * walk_page_range_debug - walk a range of pagetables not backed by a vma + * @mm: mm_struct representing the target process of page table walk + * @start: start address of the virtual address range + * @end: end address of the virtual address range + * @ops: operation to call during the walk + * @pgd: pgd to walk if different from mm->pgd + * @private: private data for callbacks' usage + * + * Similar to walk_page_range() but can walk any page tables even if they are + * not backed by VMAs. Because 'unusual' entries may be walked this function + * will also not lock the PTEs for the pte_entry() callback. + * + * This is for debugging purposes ONLY. + * + * The mmap write lock must be held. + */ +int walk_page_range_debug(struct mm_struct *mm, unsigned long start, + unsigned long end, const struct mm_walk_ops *ops, + pgd_t *pgd, void *private) +{ + struct mm_walk walk = { + .ops = ops, + .mm = mm, + .pgd = pgd, + .private = private, + .no_vma = true + }; + + /* + * When walking userland page tables, an mmap write lock must be held to + * account for munmap() downgrading to an mmap read lock when tearing + * down page tables. + * + * When walking kernel page tables, an mmap write lock must also be held + * to account for page table freeing on vmap huge page mapping. + */ + mmap_assert_write_locked(mm); + /* + * x86, arm64 ptdump allow walks of efi mm's and x86 ptdump allows walks + * of arbitrary mm's. + * + * However, they both must also hold the init_mm lock to account for + * concurrent kernel page table freeing. + */ + mmap_assert_write_locked(&init_mm); + + if (start >= end) + return -EINVAL; + if (!check_ops_safe(ops)) + return -EINVAL; + + return walk_pgd_range(start, end, &walk); +} + +int walk_page_range_vma_unsafe(struct vm_area_struct *vma, unsigned long start, + unsigned long end, const struct mm_walk_ops *ops, void *private) +{ + struct mm_walk walk = { + .ops = ops, + .mm = vma->vm_mm, + .vma = vma, + .private = private, + }; + + if (start >= end || !walk.mm) + return -EINVAL; + if (start < vma->vm_start || end > vma->vm_end) + return -EINVAL; + + process_mm_walk_lock(walk.mm, ops->walk_lock); + process_vma_walk_lock(vma, ops->walk_lock); + return __walk_page_range(start, end, &walk); +} + +int walk_page_range_vma(struct vm_area_struct *vma, unsigned long start, + unsigned long end, const struct mm_walk_ops *ops, + void *private) +{ + if (!check_ops_safe(ops)) + return -EINVAL; + + return walk_page_range_vma_unsafe(vma, start, end, ops, private); +} + +int walk_page_vma(struct vm_area_struct *vma, const struct mm_walk_ops *ops, + void *private) +{ + struct mm_walk walk = { + .ops = ops, + .mm = vma->vm_mm, + .vma = vma, + .private = private, + }; + + if (!walk.mm) + return -EINVAL; + if (!check_ops_safe(ops)) + return -EINVAL; + + process_mm_walk_lock(walk.mm, ops->walk_lock); + process_vma_walk_lock(vma, ops->walk_lock); + return __walk_page_range(vma->vm_start, vma->vm_end, &walk); +} + +/** + * walk_page_mapping - walk all memory areas mapped into a struct address_space. + * @mapping: Pointer to the struct address_space + * @first_index: First page offset in the address_space + * @nr: Number of incremental page offsets to cover + * @ops: operation to call during the walk + * @private: private data for callbacks' usage + * + * This function walks all memory areas mapped into a struct address_space. + * The walk is limited to only the given page-size index range, but if + * the index boundaries cross a huge page-table entry, that entry will be + * included. + * + * Also see walk_page_range() for additional information. + * + * Locking: + * This function can't require that the struct mm_struct::mmap_lock is held, + * since @mapping may be mapped by multiple processes. Instead + * @mapping->i_mmap_rwsem must be held. This might have implications in the + * callbacks, and it's up tho the caller to ensure that the + * struct mm_struct::mmap_lock is not needed. + * + * Also this means that a caller can't rely on the struct + * vm_area_struct::vm_flags to be constant across a call, + * except for immutable flags. Callers requiring this shouldn't use + * this function. + * + * Return: 0 on success, negative error code on failure, positive number on + * caller defined premature termination. + */ +int walk_page_mapping(struct address_space *mapping, pgoff_t first_index, + pgoff_t nr, const struct mm_walk_ops *ops, + void *private) +{ + struct mm_walk walk = { + .ops = ops, + .private = private, + }; + struct vm_area_struct *vma; + pgoff_t vba, vea, cba, cea; + unsigned long start_addr, end_addr; + int err = 0; + + if (!check_ops_safe(ops)) + return -EINVAL; + + lockdep_assert_held(&mapping->i_mmap_rwsem); + mapping_rmap_tree_foreach(vma, mapping, first_index, + first_index + nr - 1) { + /* Clip to the vma */ + vba = vma_start_pgoff(vma); + vea = vba + vma_pages(vma); + cba = first_index; + cba = max(cba, vba); + cea = first_index + nr; + cea = min(cea, vea); + + start_addr = ((cba - vba) << PAGE_SHIFT) + vma->vm_start; + end_addr = ((cea - vba) << PAGE_SHIFT) + vma->vm_start; + if (start_addr >= end_addr) + continue; + + walk.vma = vma; + walk.mm = vma->vm_mm; + + err = walk_page_test(vma->vm_start, vma->vm_end, &walk); + if (err > 0) { + err = 0; + break; + } else if (err < 0) + break; + + err = __walk_page_range(start_addr, end_addr, &walk); + if (err) + break; + } + + return err; +} + +/** + * folio_walk_start - walk the page tables to a folio + * @fw: filled with information on success. + * @vma: the VMA. + * @addr: the virtual address to use for the page table walk. + * @flags: flags modifying which folios to walk to. + * + * Walk the page tables using @addr in a given @vma to a mapped folio and + * return the folio, making sure that the page table entry referenced by + * @addr cannot change until folio_walk_end() was called. + * + * As default, this function returns only folios that are not special (e.g., not + * the zeropage) and never returns folios that are supposed to be ignored by the + * VM as documented by vm_normal_page(). If requested, zeropages will be + * returned as well. + * + * If this function returns NULL it might either indicate "there is nothing" or + * "there is nothing suitable". + * + * On success, @fw is filled and the function returns the folio while the PTL + * is still held and folio_walk_end() must be called to clean up, + * releasing any held locks. The returned folio must *not* be used after the + * call to folio_walk_end(), unless a short-term folio reference is taken before + * that call. + * + * @fw->page will correspond to the page that is effectively referenced by + * @addr. However, for shared zeropages @fw->page is set to NULL. Note that + * large folios might be mapped by multiple page table entries, and this + * function will always only lookup a single entry as specified by @addr, which + * might or might not cover more than a single page of the returned folio. + * + * This function must *not* be used as a naive replacement for + * get_user_pages() / pin_user_pages(), especially not to perform DMA or + * to carelessly modify page content. This function may *only* be used to grab + * short-term folio references, never to grab long-term folio references. + * + * Using the page table entry pointers in @fw for reading or modifying the + * entry should be avoided where possible: however, there might be valid + * use cases. + * + * WARNING: Modifying page table entries in hugetlb VMAs requires a lot of care. + * For example, PMD page table sharing might require prior unsharing. Also, + * logical hugetlb entries might span multiple physical page table entries, + * which *must* be modified in a single operation (set_huge_pte_at(), + * huge_ptep_set_*, ...). Note that the page table entry stored in @fw might + * not correspond to the first physical entry of a logical hugetlb entry. + * + * The mmap lock must be held in read mode. + * + * Return: folio pointer on success, otherwise NULL. + */ +struct folio *folio_walk_start(struct folio_walk *fw, + struct vm_area_struct *vma, unsigned long addr, + folio_walk_flags_t flags) +{ + unsigned long entry_size; + bool zeropage = false; + struct page *page; + pud_t *pudp, pud; + pmd_t *pmdp, pmd; + pte_t *ptep, pte; + spinlock_t *ptl; + pgd_t *pgdp; + p4d_t *p4dp; + + mmap_assert_locked(vma->vm_mm); + vma_pgtable_walk_begin(vma); + + if (WARN_ON_ONCE(addr < vma->vm_start || addr >= vma->vm_end)) + goto not_found; + + pgdp = pgd_offset(vma->vm_mm, addr); + if (pgd_none_or_clear_bad(pgdp)) + goto not_found; + + p4dp = p4d_offset(pgdp, addr); + if (p4d_none_or_clear_bad(p4dp)) + goto not_found; + + pudp = pud_offset(p4dp, addr); + pud = pudp_get(pudp); + if (pud_none(pud)) + goto not_found; + if (IS_ENABLED(CONFIG_PGTABLE_HAS_HUGE_LEAVES) && + (!pud_present(pud) || pud_leaf(pud))) { + ptl = pud_lock(vma->vm_mm, pudp); + pud = pudp_get(pudp); + + entry_size = PUD_SIZE; + fw->level = FW_LEVEL_PUD; + fw->pudp = pudp; + fw->pud = pud; + + if (pud_none(pud)) { + spin_unlock(ptl); + goto not_found; + } else if (pud_present(pud) && !pud_leaf(pud)) { + spin_unlock(ptl); + goto pmd_table; + } else if (pud_present(pud)) { + page = vm_normal_page_pud(vma, addr, pud); + if (page) + goto found; + } + spin_unlock(ptl); + goto not_found; + } + +pmd_table: + VM_WARN_ON_ONCE(!pud_present(pud) || pud_leaf(pud)); + pmdp = pmd_offset(pudp, addr); + pmd = pmdp_get_lockless(pmdp); + if (pmd_none(pmd)) + goto not_found; + if (IS_ENABLED(CONFIG_PGTABLE_HAS_HUGE_LEAVES) && + (!pmd_present(pmd) || pmd_leaf(pmd))) { + ptl = pmd_lock(vma->vm_mm, pmdp); + pmd = pmdp_get(pmdp); + + entry_size = PMD_SIZE; + fw->level = FW_LEVEL_PMD; + fw->pmdp = pmdp; + fw->pmd = pmd; + + if (pmd_none(pmd)) { + spin_unlock(ptl); + goto not_found; + } else if (pmd_present(pmd) && !pmd_leaf(pmd)) { + spin_unlock(ptl); + goto pte_table; + } else if (pmd_present(pmd)) { + page = vm_normal_page_pmd(vma, addr, pmd); + if (page) { + goto found; + } else if ((flags & FW_ZEROPAGE) && + is_huge_zero_pmd(pmd)) { + page = pfn_to_page(pmd_pfn(pmd)); + zeropage = true; + goto found; + } + } + spin_unlock(ptl); + goto not_found; + } + +pte_table: + VM_WARN_ON_ONCE(!pmd_present(pmd) || pmd_leaf(pmd)); + ptep = pte_offset_map_lock(vma->vm_mm, pmdp, addr, &ptl); + if (!ptep) + goto not_found; + pte = ptep_get(ptep); + + entry_size = PAGE_SIZE; + fw->level = FW_LEVEL_PTE; + fw->ptep = ptep; + fw->pte = pte; + + if (pte_present(pte)) { + page = vm_normal_page(vma, addr, pte); + if (page) + goto found; + if ((flags & FW_ZEROPAGE) && + is_zero_pfn(pte_pfn(pte))) { + page = pfn_to_page(pte_pfn(pte)); + zeropage = true; + goto found; + } + } + pte_unmap_unlock(ptep, ptl); +not_found: + vma_pgtable_walk_end(vma); + return NULL; +found: + if (!zeropage) + /* Note: Offset from the mapped page, not the folio start. */ + fw->page = page + ((addr & (entry_size - 1)) >> PAGE_SHIFT); + else + fw->page = NULL; + fw->ptl = ptl; + return page_folio(page); +} |