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b123d09304
The 8782fb61cc
("mm: pagewalk: Fix race between unmap and page walker")
introduces an assertion to walk_page_range_novma() to make all the users
of page table walker is safe. However, the race only exists for walking
the user page tables. And it is ridiculous to hold a particular user mmap
write lock against the changes of the kernel page tables. So only assert
at least mmap read lock when walking the kernel page tables. And some
users matching this case could downgrade to a mmap read lock to relief the
contention of mmap lock of init_mm, it will be nicer in hugetlb (only
holding mmap read lock) in the next patch.
Link: https://lkml.kernel.org/r/20231127084645.27017-2-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
706 lines
19 KiB
C
706 lines
19 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/pagewalk.h>
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#include <linux/highmem.h>
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#include <linux/sched.h>
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#include <linux/hugetlb.h>
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/*
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* We want to know the real level where a entry is located ignoring any
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* folding of levels which may be happening. For example if p4d is folded then
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* a missing entry found at level 1 (p4d) is actually at level 0 (pgd).
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*/
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static int real_depth(int depth)
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{
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if (depth == 3 && PTRS_PER_PMD == 1)
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depth = 2;
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if (depth == 2 && PTRS_PER_PUD == 1)
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depth = 1;
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if (depth == 1 && PTRS_PER_P4D == 1)
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depth = 0;
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return depth;
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}
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static int walk_pte_range_inner(pte_t *pte, unsigned long addr,
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unsigned long end, struct mm_walk *walk)
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{
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const struct mm_walk_ops *ops = walk->ops;
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int err = 0;
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for (;;) {
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err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
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if (err)
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break;
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if (addr >= end - PAGE_SIZE)
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break;
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addr += PAGE_SIZE;
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pte++;
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}
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return err;
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}
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static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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pte_t *pte;
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int err = 0;
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spinlock_t *ptl;
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if (walk->no_vma) {
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/*
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* pte_offset_map() might apply user-specific validation.
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* Indeed, on x86_64 the pmd entries set up by init_espfix_ap()
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* fit its pmd_bad() check (_PAGE_NX set and _PAGE_RW clear),
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* and CONFIG_EFI_PGT_DUMP efi_mm goes so far as to walk them.
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*/
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if (walk->mm == &init_mm || addr >= TASK_SIZE)
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pte = pte_offset_kernel(pmd, addr);
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else
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pte = pte_offset_map(pmd, addr);
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if (pte) {
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err = walk_pte_range_inner(pte, addr, end, walk);
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if (walk->mm != &init_mm && addr < TASK_SIZE)
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pte_unmap(pte);
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}
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} else {
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pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
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if (pte) {
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err = walk_pte_range_inner(pte, addr, end, walk);
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pte_unmap_unlock(pte, ptl);
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}
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}
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if (!pte)
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walk->action = ACTION_AGAIN;
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return err;
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}
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#ifdef CONFIG_ARCH_HAS_HUGEPD
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static int walk_hugepd_range(hugepd_t *phpd, unsigned long addr,
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unsigned long end, struct mm_walk *walk, int pdshift)
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{
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int err = 0;
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const struct mm_walk_ops *ops = walk->ops;
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int shift = hugepd_shift(*phpd);
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int page_size = 1 << shift;
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if (!ops->pte_entry)
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return 0;
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if (addr & (page_size - 1))
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return 0;
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for (;;) {
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pte_t *pte;
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spin_lock(&walk->mm->page_table_lock);
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pte = hugepte_offset(*phpd, addr, pdshift);
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err = ops->pte_entry(pte, addr, addr + page_size, walk);
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spin_unlock(&walk->mm->page_table_lock);
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if (err)
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break;
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if (addr >= end - page_size)
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break;
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addr += page_size;
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}
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return err;
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}
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#else
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static int walk_hugepd_range(hugepd_t *phpd, unsigned long addr,
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unsigned long end, struct mm_walk *walk, int pdshift)
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{
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return 0;
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}
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#endif
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static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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pmd_t *pmd;
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unsigned long next;
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const struct mm_walk_ops *ops = walk->ops;
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int err = 0;
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int depth = real_depth(3);
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pmd = pmd_offset(pud, addr);
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do {
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again:
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next = pmd_addr_end(addr, end);
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if (pmd_none(*pmd)) {
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if (ops->pte_hole)
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err = ops->pte_hole(addr, next, depth, walk);
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if (err)
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break;
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continue;
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}
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walk->action = ACTION_SUBTREE;
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/*
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* This implies that each ->pmd_entry() handler
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* needs to know about pmd_trans_huge() pmds
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*/
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if (ops->pmd_entry)
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err = ops->pmd_entry(pmd, addr, next, walk);
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if (err)
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break;
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if (walk->action == ACTION_AGAIN)
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goto again;
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/*
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* Check this here so we only break down trans_huge
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* pages when we _need_ to
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*/
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if ((!walk->vma && (pmd_leaf(*pmd) || !pmd_present(*pmd))) ||
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walk->action == ACTION_CONTINUE ||
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!(ops->pte_entry))
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continue;
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if (walk->vma)
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split_huge_pmd(walk->vma, pmd, addr);
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if (is_hugepd(__hugepd(pmd_val(*pmd))))
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err = walk_hugepd_range((hugepd_t *)pmd, addr, next, walk, PMD_SHIFT);
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else
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err = walk_pte_range(pmd, addr, next, walk);
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if (err)
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break;
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if (walk->action == ACTION_AGAIN)
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goto again;
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} while (pmd++, addr = next, addr != end);
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return err;
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}
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static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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pud_t *pud;
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unsigned long next;
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const struct mm_walk_ops *ops = walk->ops;
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int err = 0;
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int depth = real_depth(2);
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pud = pud_offset(p4d, addr);
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do {
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again:
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next = pud_addr_end(addr, end);
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if (pud_none(*pud)) {
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if (ops->pte_hole)
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err = ops->pte_hole(addr, next, depth, walk);
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if (err)
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break;
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continue;
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}
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walk->action = ACTION_SUBTREE;
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if (ops->pud_entry)
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err = ops->pud_entry(pud, addr, next, walk);
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if (err)
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break;
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if (walk->action == ACTION_AGAIN)
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goto again;
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if ((!walk->vma && (pud_leaf(*pud) || !pud_present(*pud))) ||
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walk->action == ACTION_CONTINUE ||
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!(ops->pmd_entry || ops->pte_entry))
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continue;
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if (walk->vma)
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split_huge_pud(walk->vma, pud, addr);
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if (pud_none(*pud))
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goto again;
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if (is_hugepd(__hugepd(pud_val(*pud))))
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err = walk_hugepd_range((hugepd_t *)pud, addr, next, walk, PUD_SHIFT);
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else
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err = walk_pmd_range(pud, addr, next, walk);
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if (err)
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break;
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} while (pud++, addr = next, addr != end);
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return err;
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}
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static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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p4d_t *p4d;
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unsigned long next;
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const struct mm_walk_ops *ops = walk->ops;
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int err = 0;
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int depth = real_depth(1);
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p4d = p4d_offset(pgd, addr);
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do {
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next = p4d_addr_end(addr, end);
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if (p4d_none_or_clear_bad(p4d)) {
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if (ops->pte_hole)
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err = ops->pte_hole(addr, next, depth, walk);
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if (err)
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break;
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continue;
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}
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if (ops->p4d_entry) {
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err = ops->p4d_entry(p4d, addr, next, walk);
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if (err)
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break;
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}
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if (is_hugepd(__hugepd(p4d_val(*p4d))))
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err = walk_hugepd_range((hugepd_t *)p4d, addr, next, walk, P4D_SHIFT);
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else if (ops->pud_entry || ops->pmd_entry || ops->pte_entry)
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err = walk_pud_range(p4d, addr, next, walk);
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if (err)
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break;
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} while (p4d++, addr = next, addr != end);
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return err;
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}
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static int walk_pgd_range(unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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pgd_t *pgd;
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unsigned long next;
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const struct mm_walk_ops *ops = walk->ops;
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int err = 0;
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if (walk->pgd)
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pgd = walk->pgd + pgd_index(addr);
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else
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pgd = pgd_offset(walk->mm, addr);
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do {
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next = pgd_addr_end(addr, end);
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if (pgd_none_or_clear_bad(pgd)) {
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if (ops->pte_hole)
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err = ops->pte_hole(addr, next, 0, walk);
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if (err)
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break;
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continue;
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}
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if (ops->pgd_entry) {
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err = ops->pgd_entry(pgd, addr, next, walk);
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if (err)
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break;
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}
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if (is_hugepd(__hugepd(pgd_val(*pgd))))
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err = walk_hugepd_range((hugepd_t *)pgd, addr, next, walk, PGDIR_SHIFT);
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else if (ops->p4d_entry || ops->pud_entry || ops->pmd_entry || ops->pte_entry)
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err = walk_p4d_range(pgd, addr, next, walk);
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if (err)
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break;
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} while (pgd++, addr = next, addr != end);
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return err;
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}
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#ifdef CONFIG_HUGETLB_PAGE
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static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
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unsigned long end)
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{
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unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
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return boundary < end ? boundary : end;
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}
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static int walk_hugetlb_range(unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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struct vm_area_struct *vma = walk->vma;
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struct hstate *h = hstate_vma(vma);
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unsigned long next;
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unsigned long hmask = huge_page_mask(h);
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unsigned long sz = huge_page_size(h);
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pte_t *pte;
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const struct mm_walk_ops *ops = walk->ops;
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int err = 0;
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hugetlb_vma_lock_read(vma);
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do {
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next = hugetlb_entry_end(h, addr, end);
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pte = hugetlb_walk(vma, addr & hmask, sz);
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if (pte)
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err = ops->hugetlb_entry(pte, hmask, addr, next, walk);
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else if (ops->pte_hole)
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err = ops->pte_hole(addr, next, -1, walk);
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if (err)
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break;
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} while (addr = next, addr != end);
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hugetlb_vma_unlock_read(vma);
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return err;
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}
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#else /* CONFIG_HUGETLB_PAGE */
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static int walk_hugetlb_range(unsigned long addr, unsigned long end,
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struct mm_walk *walk)
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{
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return 0;
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}
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#endif /* CONFIG_HUGETLB_PAGE */
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/*
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* Decide whether we really walk over the current vma on [@start, @end)
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* or skip it via the returned value. Return 0 if we do walk over the
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* current vma, and return 1 if we skip the vma. Negative values means
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* error, where we abort the current walk.
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*/
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static int walk_page_test(unsigned long start, unsigned long end,
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struct mm_walk *walk)
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{
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struct vm_area_struct *vma = walk->vma;
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const struct mm_walk_ops *ops = walk->ops;
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if (ops->test_walk)
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return ops->test_walk(start, end, walk);
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/*
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* vma(VM_PFNMAP) doesn't have any valid struct pages behind VM_PFNMAP
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* range, so we don't walk over it as we do for normal vmas. However,
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* Some callers are interested in handling hole range and they don't
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* want to just ignore any single address range. Such users certainly
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* define their ->pte_hole() callbacks, so let's delegate them to handle
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* vma(VM_PFNMAP).
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*/
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if (vma->vm_flags & VM_PFNMAP) {
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int err = 1;
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if (ops->pte_hole)
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err = ops->pte_hole(start, end, -1, walk);
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return err ? err : 1;
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}
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return 0;
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}
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static int __walk_page_range(unsigned long start, unsigned long end,
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struct mm_walk *walk)
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{
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int err = 0;
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struct vm_area_struct *vma = walk->vma;
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const struct mm_walk_ops *ops = walk->ops;
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if (ops->pre_vma) {
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err = ops->pre_vma(start, end, walk);
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if (err)
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return err;
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}
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if (is_vm_hugetlb_page(vma)) {
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if (ops->hugetlb_entry)
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err = walk_hugetlb_range(start, end, walk);
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} else
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err = walk_pgd_range(start, end, walk);
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if (ops->post_vma)
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ops->post_vma(walk);
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return err;
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}
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static inline void process_mm_walk_lock(struct mm_struct *mm,
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enum page_walk_lock walk_lock)
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{
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if (walk_lock == PGWALK_RDLOCK)
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mmap_assert_locked(mm);
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else
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mmap_assert_write_locked(mm);
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}
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static inline void process_vma_walk_lock(struct vm_area_struct *vma,
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enum page_walk_lock walk_lock)
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{
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#ifdef CONFIG_PER_VMA_LOCK
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switch (walk_lock) {
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case PGWALK_WRLOCK:
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vma_start_write(vma);
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break;
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case PGWALK_WRLOCK_VERIFY:
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vma_assert_write_locked(vma);
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break;
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case PGWALK_RDLOCK:
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/* PGWALK_RDLOCK is handled by process_mm_walk_lock */
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break;
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}
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#endif
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}
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/**
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* walk_page_range - walk page table with caller specific callbacks
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* @mm: mm_struct representing the target process of page table walk
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* @start: start address of the virtual address range
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* @end: end address of the virtual address range
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* @ops: operation to call during the walk
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* @private: private data for callbacks' usage
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*
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* Recursively walk the page table tree of the process represented by @mm
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* within the virtual address range [@start, @end). During walking, we can do
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* some caller-specific works for each entry, by setting up pmd_entry(),
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* pte_entry(), and/or hugetlb_entry(). If you don't set up for some of these
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* callbacks, the associated entries/pages are just ignored.
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* The return values of these callbacks are commonly defined like below:
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*
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* - 0 : succeeded to handle the current entry, and if you don't reach the
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* end address yet, continue to walk.
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* - >0 : succeeded to handle the current entry, and return to the caller
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* with caller specific value.
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* - <0 : failed to handle the current entry, and return to the caller
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* with error code.
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*
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* Before starting to walk page table, some callers want to check whether
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* they really want to walk over the current vma, typically by checking
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* its vm_flags. walk_page_test() and @ops->test_walk() are used for this
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* purpose.
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*
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* If operations need to be staged before and committed after a vma is walked,
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* there are two callbacks, pre_vma() and post_vma(). Note that post_vma(),
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* since it is intended to handle commit-type operations, can't return any
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* errors.
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*
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* struct mm_walk keeps current values of some common data like vma and pmd,
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* which are useful for the access from callbacks. If you want to pass some
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* caller-specific data to callbacks, @private should be helpful.
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*
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* Locking:
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* Callers of walk_page_range() and walk_page_vma() should hold @mm->mmap_lock,
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* because these function traverse vma list and/or access to vma's data.
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*/
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int walk_page_range(struct mm_struct *mm, unsigned long start,
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unsigned long end, const struct mm_walk_ops *ops,
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void *private)
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{
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int err = 0;
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unsigned long next;
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struct vm_area_struct *vma;
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struct mm_walk walk = {
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.ops = ops,
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.mm = mm,
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.private = private,
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};
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if (start >= end)
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return -EINVAL;
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if (!walk.mm)
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return -EINVAL;
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process_mm_walk_lock(walk.mm, ops->walk_lock);
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vma = find_vma(walk.mm, start);
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do {
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if (!vma) { /* after the last vma */
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|
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;
|
|
}
|
|
|
|
/**
|
|
* walk_page_range_novma - 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 useful for
|
|
* walking the 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 approache (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_page_range_novma(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
|
|
};
|
|
|
|
if (start >= end || !walk.mm)
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* 1) For walking the user virtual address space:
|
|
*
|
|
* 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 hold.
|
|
*
|
|
* 2) For walking the kernel virtual address space:
|
|
*
|
|
* The kernel intermediate page tables usually do not be freed, so
|
|
* the mmap map 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.
|
|
*/
|
|
if (mm == &init_mm)
|
|
mmap_assert_locked(walk.mm);
|
|
else
|
|
mmap_assert_write_locked(walk.mm);
|
|
|
|
return walk_pgd_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)
|
|
{
|
|
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_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;
|
|
|
|
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;
|
|
|
|
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;
|
|
}
|