diff options
Diffstat (limited to 'mm/pagewalk.c')
| -rw-r--r-- | mm/pagewalk.c | 901 |
1 files changed, 791 insertions, 110 deletions
diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 1a4197965415..90cc346a6ecf 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -1,26 +1,96 @@ -#include <linux/mm.h> +// 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 <linux/leafops.h> -static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, - struct mm_walk *walk) +#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) { - pte_t *pte; + 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; - pte = pte_offset_map(pmd, addr); for (;;) { - err = walk->pte_entry(pte, addr, addr + PAGE_SIZE, walk); - if (err) - break; - addr += PAGE_SIZE; - if (addr == end) + 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; - pte_unmap(pte); + 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; } @@ -29,41 +99,66 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, { 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); pmd = pmd_offset(pud, addr); do { again: next = pmd_addr_end(addr, end); - if (pmd_none(*pmd) || !walk->vma) { - if (walk->pte_hole) - err = walk->pte_hole(addr, next, walk); + 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; - continue; + if (!has_install) + continue; } + + walk->action = ACTION_SUBTREE; + /* * This implies that each ->pmd_entry() handler * needs to know about pmd_trans_huge() pmds */ - if (walk->pmd_entry) - err = walk->pmd_entry(pmd, addr, next, walk); + if (ops->pmd_entry) + err = ops->pmd_entry(pmd, addr, next, walk); if (err) break; - /* - * Check this here so we only break down trans_huge - * pages when we _need_ to - */ - if (!walk->pte_entry) + if (walk->action == ACTION_AGAIN) + goto again; + if (walk->action == ACTION_CONTINUE) continue; - split_huge_pmd(walk->vma, pmd, addr); - if (pmd_trans_unstable(pmd)) - goto again; + 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; @@ -74,38 +169,59 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, { 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: next = pud_addr_end(addr, end); - if (pud_none(*pud) || !walk->vma) { - if (walk->pte_hole) - err = walk->pte_hole(addr, next, walk); + 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; - continue; + if (!has_install) + continue; } - if (walk->pud_entry) { - spinlock_t *ptl = pud_trans_huge_lock(pud, walk->vma); + walk->action = ACTION_SUBTREE; - if (ptl) { - err = walk->pud_entry(pud, addr, next, walk); - spin_unlock(ptl); - if (err) - break; + 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; - } } - split_huge_pud(walk->vma, pud, addr); + if (walk->vma) + split_huge_pud(walk->vma, pud, addr); + else if (pud_leaf(*pud) || !pud_present(*pud)) + continue; /* Nothing to do. */ + if (pud_none(*pud)) goto again; - if (walk->pmd_entry || walk->pte_entry) - err = walk_pmd_range(pud, addr, next, walk); + err = walk_pmd_range(pud, addr, next, walk); if (err) break; } while (pud++, addr = next, addr != end); @@ -118,19 +234,31 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end, { 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 (walk->pte_hole) - err = walk->pte_hole(addr, next, walk); + 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; - continue; } - if (walk->pmd_entry || walk->pte_entry) + if (has_handler || has_install) err = walk_pud_range(p4d, addr, next, walk); if (err) break; @@ -144,19 +272,34 @@ static int walk_pgd_range(unsigned long addr, unsigned long end, { 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; - pgd = pgd_offset(walk->mm, addr); + 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 (walk->pte_hole) - err = walk->pte_hole(addr, next, walk); + 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; - continue; + if (!has_install) + continue; } - if (walk->pmd_entry || walk->pte_entry) + 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; @@ -182,16 +325,21 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end, 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 = huge_pte_offset(walk->mm, addr & hmask, sz); - if (pte && walk->hugetlb_entry) - err = walk->hugetlb_entry(pte, hmask, addr, next, walk); + 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; } @@ -215,9 +363,10 @@ 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 (walk->test_walk) - return walk->test_walk(start, end, walk); + if (ops->test_walk) + return ops->test_walk(start, end, walk); /* * vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP @@ -229,8 +378,8 @@ static int walk_page_test(unsigned long start, unsigned long end, */ if (vma->vm_flags & VM_PFNMAP) { int err = 1; - if (walk->pte_hole) - err = walk->pte_hole(start, end, walk); + if (ops->pte_hole) + err = ops->pte_hole(start, end, -1, walk); return err ? err : 1; } return 0; @@ -241,75 +390,108 @@ static int __walk_page_range(unsigned long start, unsigned long end, { 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); - if (vma && is_vm_hugetlb_page(vma)) { - if (walk->hugetlb_entry) + /* 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; } -/** - * walk_page_range - walk page table with caller specific callbacks - * - * Recursively walk the page table tree of the process represented by @walk->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 @walk->test_walk() are used for this - * purpose. - * - * 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, @walk->private should be helpful. +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. * - * Locking: - * Callers of walk_page_range() and walk_page_vma() should hold - * @walk->mm->mmap_sem, because these function traverse vma list and/or - * access to vma's data. + * 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(unsigned long start, unsigned long end, - struct mm_walk *walk) +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) + if (!walk.mm) return -EINVAL; - VM_BUG_ON_MM(!rwsem_is_locked(&walk->mm->mmap_sem), walk->mm); + process_mm_walk_lock(walk.mm, ops->walk_lock); - vma = find_vma(walk->mm, start); + vma = find_vma(walk.mm, start); do { if (!vma) { /* after the last vma */ - walk->vma = NULL; + 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; + walk.vma = NULL; next = min(end, vma->vm_start); + if (ops->pte_hole) + err = ops->pte_hole(start, next, -1, &walk); } else { /* inside vma */ - walk->vma = vma; + process_vma_walk_lock(vma, ops->walk_lock); + walk.vma = vma; next = min(end, vma->vm_end); - vma = vma->vm_next; + vma = find_vma(mm, vma->vm_end); - err = walk_page_test(start, next, walk); + err = walk_page_test(start, next, &walk); if (err > 0) { /* * positive return values are purely for @@ -321,29 +503,528 @@ int walk_page_range(unsigned long start, unsigned long end, } if (err < 0) break; + err = __walk_page_range(start, next, &walk); } - if (walk->vma || walk->pte_hole) - err = __walk_page_range(start, next, walk); if (err) break; } while (start = next, start < end); return err; } -int walk_page_vma(struct vm_area_struct *vma, struct mm_walk *walk) +/* + * 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) { - int err; + /* + * 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; +} - if (!walk->mm) +/** + * 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. + */ +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 + }; + + /* For convenience, we allow traversal of kernel mappings. */ + if (mm == &init_mm) + return walk_kernel_page_table_range(start, end, ops, + pgd, private); + if (start >= end || !walk.mm) + return -EINVAL; + if (!check_ops_safe(ops)) + return -EINVAL; + + /* + * The mmap lock protects the page walker from changes to the page + * tables during the walk. However a read lock is insufficient to + * protect those areas which don't have a VMA as munmap() detaches + * the VMAs before downgrading to a read lock and actually tearing + * down PTEs/page tables. In which case, the mmap write lock should + * be held. + */ + mmap_assert_write_locked(mm); + + 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; - VM_BUG_ON(!rwsem_is_locked(&walk->mm->mmap_sem)); - VM_BUG_ON(!vma); - walk->vma = vma; - err = walk_page_test(vma->vm_start, vma->vm_end, walk); - if (err > 0) - return 0; - if (err < 0) - return err; - return __walk_page_range(vma->vm_start, vma->vm_end, walk); + lockdep_assert_held(&mapping->i_mmap_rwsem); + vma_interval_tree_foreach(vma, &mapping->i_mmap, first_index, + first_index + nr - 1) { + /* Clip to the vma */ + vba = vma->vm_pgoff; + 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. + * + * As default, this function only considers present page table entries. + * If requested, it will also consider migration entries. + * + * 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 migration entries and 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 expose_page = true; + 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; + } + /* + * TODO: FW_MIGRATION support for PUD migration entries + * once there are relevant users. + */ + 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)); + expose_page = false; + goto found; + } + } else if ((flags & FW_MIGRATION) && + pmd_is_migration_entry(pmd)) { + const softleaf_t entry = softleaf_from_pmd(pmd); + + page = softleaf_to_page(entry); + expose_page = false; + 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)); + expose_page = false; + goto found; + } + } else if (!pte_none(pte)) { + const softleaf_t entry = softleaf_from_pte(pte); + + if ((flags & FW_MIGRATION) && softleaf_is_migration(entry)) { + page = softleaf_to_page(entry); + expose_page = false; + goto found; + } + } + pte_unmap_unlock(ptep, ptl); +not_found: + vma_pgtable_walk_end(vma); + return NULL; +found: + if (expose_page) + /* 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); } |