// 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:
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;
}
walk->action = ACTION_SUBTREE;
/*
* 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:
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;
}
walk->action = ACTION_SUBTREE;
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);
}
