diff options
Diffstat (limited to 'mm/userfaultfd.c')
| -rw-r--r-- | mm/userfaultfd.c | 614 |
1 files changed, 614 insertions, 0 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 0b6ca553bebe..9ec814e47e99 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -842,3 +842,617 @@ out_unlock: mmap_read_unlock(dst_mm); return err; } + + +void double_pt_lock(spinlock_t *ptl1, + spinlock_t *ptl2) + __acquires(ptl1) + __acquires(ptl2) +{ + spinlock_t *ptl_tmp; + + if (ptl1 > ptl2) { + /* exchange ptl1 and ptl2 */ + ptl_tmp = ptl1; + ptl1 = ptl2; + ptl2 = ptl_tmp; + } + /* lock in virtual address order to avoid lock inversion */ + spin_lock(ptl1); + if (ptl1 != ptl2) + spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING); + else + __acquire(ptl2); +} + +void double_pt_unlock(spinlock_t *ptl1, + spinlock_t *ptl2) + __releases(ptl1) + __releases(ptl2) +{ + spin_unlock(ptl1); + if (ptl1 != ptl2) + spin_unlock(ptl2); + else + __release(ptl2); +} + + +static int move_present_pte(struct mm_struct *mm, + struct vm_area_struct *dst_vma, + struct vm_area_struct *src_vma, + unsigned long dst_addr, unsigned long src_addr, + pte_t *dst_pte, pte_t *src_pte, + pte_t orig_dst_pte, pte_t orig_src_pte, + spinlock_t *dst_ptl, spinlock_t *src_ptl, + struct folio *src_folio) +{ + int err = 0; + + double_pt_lock(dst_ptl, src_ptl); + + if (!pte_same(*src_pte, orig_src_pte) || + !pte_same(*dst_pte, orig_dst_pte)) { + err = -EAGAIN; + goto out; + } + if (folio_test_large(src_folio) || + folio_maybe_dma_pinned(src_folio) || + !PageAnonExclusive(&src_folio->page)) { + err = -EBUSY; + goto out; + } + + folio_move_anon_rmap(src_folio, dst_vma); + WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr)); + + orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte); + /* Folio got pinned from under us. Put it back and fail the move. */ + if (folio_maybe_dma_pinned(src_folio)) { + set_pte_at(mm, src_addr, src_pte, orig_src_pte); + err = -EBUSY; + goto out; + } + + orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot); + /* Follow mremap() behavior and treat the entry dirty after the move */ + orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma); + + set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte); +out: + double_pt_unlock(dst_ptl, src_ptl); + return err; +} + +static int move_swap_pte(struct mm_struct *mm, + unsigned long dst_addr, unsigned long src_addr, + pte_t *dst_pte, pte_t *src_pte, + pte_t orig_dst_pte, pte_t orig_src_pte, + spinlock_t *dst_ptl, spinlock_t *src_ptl) +{ + if (!pte_swp_exclusive(orig_src_pte)) + return -EBUSY; + + double_pt_lock(dst_ptl, src_ptl); + + if (!pte_same(*src_pte, orig_src_pte) || + !pte_same(*dst_pte, orig_dst_pte)) { + double_pt_unlock(dst_ptl, src_ptl); + return -EAGAIN; + } + + orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); + set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); + double_pt_unlock(dst_ptl, src_ptl); + + return 0; +} + +/* + * The mmap_lock for reading is held by the caller. Just move the page + * from src_pmd to dst_pmd if possible, and return true if succeeded + * in moving the page. + */ +static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, + struct vm_area_struct *dst_vma, + struct vm_area_struct *src_vma, + unsigned long dst_addr, unsigned long src_addr, + __u64 mode) +{ + swp_entry_t entry; + pte_t orig_src_pte, orig_dst_pte; + pte_t src_folio_pte; + spinlock_t *src_ptl, *dst_ptl; + pte_t *src_pte = NULL; + pte_t *dst_pte = NULL; + + struct folio *src_folio = NULL; + struct anon_vma *src_anon_vma = NULL; + struct mmu_notifier_range range; + int err = 0; + + flush_cache_range(src_vma, src_addr, src_addr + PAGE_SIZE); + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, + src_addr, src_addr + PAGE_SIZE); + mmu_notifier_invalidate_range_start(&range); +retry: + dst_pte = pte_offset_map_nolock(mm, dst_pmd, dst_addr, &dst_ptl); + + /* Retry if a huge pmd materialized from under us */ + if (unlikely(!dst_pte)) { + err = -EAGAIN; + goto out; + } + + src_pte = pte_offset_map_nolock(mm, src_pmd, src_addr, &src_ptl); + + /* + * We held the mmap_lock for reading so MADV_DONTNEED + * can zap transparent huge pages under us, or the + * transparent huge page fault can establish new + * transparent huge pages under us. + */ + if (unlikely(!src_pte)) { + err = -EAGAIN; + goto out; + } + + /* Sanity checks before the operation */ + if (WARN_ON_ONCE(pmd_none(*dst_pmd)) || WARN_ON_ONCE(pmd_none(*src_pmd)) || + WARN_ON_ONCE(pmd_trans_huge(*dst_pmd)) || WARN_ON_ONCE(pmd_trans_huge(*src_pmd))) { + err = -EINVAL; + goto out; + } + + spin_lock(dst_ptl); + orig_dst_pte = *dst_pte; + spin_unlock(dst_ptl); + if (!pte_none(orig_dst_pte)) { + err = -EEXIST; + goto out; + } + + spin_lock(src_ptl); + orig_src_pte = *src_pte; + spin_unlock(src_ptl); + if (pte_none(orig_src_pte)) { + if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) + err = -ENOENT; + else /* nothing to do to move a hole */ + err = 0; + goto out; + } + + /* If PTE changed after we locked the folio them start over */ + if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) { + err = -EAGAIN; + goto out; + } + + if (pte_present(orig_src_pte)) { + /* + * Pin and lock both source folio and anon_vma. Since we are in + * RCU read section, we can't block, so on contention have to + * unmap the ptes, obtain the lock and retry. + */ + if (!src_folio) { + struct folio *folio; + + /* + * Pin the page while holding the lock to be sure the + * page isn't freed under us + */ + spin_lock(src_ptl); + if (!pte_same(orig_src_pte, *src_pte)) { + spin_unlock(src_ptl); + err = -EAGAIN; + goto out; + } + + folio = vm_normal_folio(src_vma, src_addr, orig_src_pte); + if (!folio || !PageAnonExclusive(&folio->page)) { + spin_unlock(src_ptl); + err = -EBUSY; + goto out; + } + + folio_get(folio); + src_folio = folio; + src_folio_pte = orig_src_pte; + spin_unlock(src_ptl); + + if (!folio_trylock(src_folio)) { + pte_unmap(&orig_src_pte); + pte_unmap(&orig_dst_pte); + src_pte = dst_pte = NULL; + /* now we can block and wait */ + folio_lock(src_folio); + goto retry; + } + + if (WARN_ON_ONCE(!folio_test_anon(src_folio))) { + err = -EBUSY; + goto out; + } + } + + /* at this point we have src_folio locked */ + if (folio_test_large(src_folio)) { + err = split_folio(src_folio); + if (err) + goto out; + } + + if (!src_anon_vma) { + /* + * folio_referenced walks the anon_vma chain + * without the folio lock. Serialize against it with + * the anon_vma lock, the folio lock is not enough. + */ + src_anon_vma = folio_get_anon_vma(src_folio); + if (!src_anon_vma) { + /* page was unmapped from under us */ + err = -EAGAIN; + goto out; + } + if (!anon_vma_trylock_write(src_anon_vma)) { + pte_unmap(&orig_src_pte); + pte_unmap(&orig_dst_pte); + src_pte = dst_pte = NULL; + /* now we can block and wait */ + anon_vma_lock_write(src_anon_vma); + goto retry; + } + } + + err = move_present_pte(mm, dst_vma, src_vma, + dst_addr, src_addr, dst_pte, src_pte, + orig_dst_pte, orig_src_pte, + dst_ptl, src_ptl, src_folio); + } else { + entry = pte_to_swp_entry(orig_src_pte); + if (non_swap_entry(entry)) { + if (is_migration_entry(entry)) { + pte_unmap(&orig_src_pte); + pte_unmap(&orig_dst_pte); + src_pte = dst_pte = NULL; + migration_entry_wait(mm, src_pmd, src_addr); + err = -EAGAIN; + } else + err = -EFAULT; + goto out; + } + + err = move_swap_pte(mm, dst_addr, src_addr, + dst_pte, src_pte, + orig_dst_pte, orig_src_pte, + dst_ptl, src_ptl); + } + +out: + if (src_anon_vma) { + anon_vma_unlock_write(src_anon_vma); + put_anon_vma(src_anon_vma); + } + if (src_folio) { + folio_unlock(src_folio); + folio_put(src_folio); + } + if (dst_pte) + pte_unmap(dst_pte); + if (src_pte) + pte_unmap(src_pte); + mmu_notifier_invalidate_range_end(&range); + + return err; +} + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE +static inline bool move_splits_huge_pmd(unsigned long dst_addr, + unsigned long src_addr, + unsigned long src_end) +{ + return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) || + src_end - src_addr < HPAGE_PMD_SIZE; +} +#else +static inline bool move_splits_huge_pmd(unsigned long dst_addr, + unsigned long src_addr, + unsigned long src_end) +{ + /* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */ + return false; +} +#endif + +static inline bool vma_move_compatible(struct vm_area_struct *vma) +{ + return !(vma->vm_flags & (VM_PFNMAP | VM_IO | VM_HUGETLB | + VM_MIXEDMAP | VM_SHADOW_STACK)); +} + +static int validate_move_areas(struct userfaultfd_ctx *ctx, + struct vm_area_struct *src_vma, + struct vm_area_struct *dst_vma) +{ + /* Only allow moving if both have the same access and protection */ + if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) || + pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot)) + return -EINVAL; + + /* Only allow moving if both are mlocked or both aren't */ + if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED)) + return -EINVAL; + + /* + * For now, we keep it simple and only move between writable VMAs. + * Access flags are equal, therefore cheching only the source is enough. + */ + if (!(src_vma->vm_flags & VM_WRITE)) + return -EINVAL; + + /* Check if vma flags indicate content which can be moved */ + if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma)) + return -EINVAL; + + /* Ensure dst_vma is registered in uffd we are operating on */ + if (!dst_vma->vm_userfaultfd_ctx.ctx || + dst_vma->vm_userfaultfd_ctx.ctx != ctx) + return -EINVAL; + + /* Only allow moving across anonymous vmas */ + if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma)) + return -EINVAL; + + /* + * Ensure the dst_vma has a anon_vma or this page + * would get a NULL anon_vma when moved in the + * dst_vma. + */ + if (unlikely(anon_vma_prepare(dst_vma))) + return -ENOMEM; + + return 0; +} + +/** + * move_pages - move arbitrary anonymous pages of an existing vma + * @ctx: pointer to the userfaultfd context + * @mm: the address space to move pages + * @dst_start: start of the destination virtual memory range + * @src_start: start of the source virtual memory range + * @len: length of the virtual memory range + * @mode: flags from uffdio_move.mode + * + * Must be called with mmap_lock held for read. + * + * move_pages() remaps arbitrary anonymous pages atomically in zero + * copy. It only works on non shared anonymous pages because those can + * be relocated without generating non linear anon_vmas in the rmap + * code. + * + * It provides a zero copy mechanism to handle userspace page faults. + * The source vma pages should have mapcount == 1, which can be + * enforced by using madvise(MADV_DONTFORK) on src vma. + * + * The thread receiving the page during the userland page fault + * will receive the faulting page in the source vma through the network, + * storage or any other I/O device (MADV_DONTFORK in the source vma + * avoids move_pages() to fail with -EBUSY if the process forks before + * move_pages() is called), then it will call move_pages() to map the + * page in the faulting address in the destination vma. + * + * This userfaultfd command works purely via pagetables, so it's the + * most efficient way to move physical non shared anonymous pages + * across different virtual addresses. Unlike mremap()/mmap()/munmap() + * it does not create any new vmas. The mapping in the destination + * address is atomic. + * + * It only works if the vma protection bits are identical from the + * source and destination vma. + * + * It can remap non shared anonymous pages within the same vma too. + * + * If the source virtual memory range has any unmapped holes, or if + * the destination virtual memory range is not a whole unmapped hole, + * move_pages() will fail respectively with -ENOENT or -EEXIST. This + * provides a very strict behavior to avoid any chance of memory + * corruption going unnoticed if there are userland race conditions. + * Only one thread should resolve the userland page fault at any given + * time for any given faulting address. This means that if two threads + * try to both call move_pages() on the same destination address at the + * same time, the second thread will get an explicit error from this + * command. + * + * The command retval will return "len" is successful. The command + * however can be interrupted by fatal signals or errors. If + * interrupted it will return the number of bytes successfully + * remapped before the interruption if any, or the negative error if + * none. It will never return zero. Either it will return an error or + * an amount of bytes successfully moved. If the retval reports a + * "short" remap, the move_pages() command should be repeated by + * userland with src+retval, dst+reval, len-retval if it wants to know + * about the error that interrupted it. + * + * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to + * prevent -ENOENT errors to materialize if there are holes in the + * source virtual range that is being remapped. The holes will be + * accounted as successfully remapped in the retval of the + * command. This is mostly useful to remap hugepage naturally aligned + * virtual regions without knowing if there are transparent hugepage + * in the regions or not, but preventing the risk of having to split + * the hugepmd during the remap. + * + * If there's any rmap walk that is taking the anon_vma locks without + * first obtaining the folio lock (the only current instance is + * folio_referenced), they will have to verify if the folio->mapping + * has changed after taking the anon_vma lock. If it changed they + * should release the lock and retry obtaining a new anon_vma, because + * it means the anon_vma was changed by move_pages() before the lock + * could be obtained. This is the only additional complexity added to + * the rmap code to provide this anonymous page remapping functionality. + */ +ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm, + unsigned long dst_start, unsigned long src_start, + unsigned long len, __u64 mode) +{ + struct vm_area_struct *src_vma, *dst_vma; + unsigned long src_addr, dst_addr; + pmd_t *src_pmd, *dst_pmd; + long err = -EINVAL; + ssize_t moved = 0; + + /* Sanitize the command parameters. */ + if (WARN_ON_ONCE(src_start & ~PAGE_MASK) || + WARN_ON_ONCE(dst_start & ~PAGE_MASK) || + WARN_ON_ONCE(len & ~PAGE_MASK)) + goto out; + + /* Does the address range wrap, or is the span zero-sized? */ + if (WARN_ON_ONCE(src_start + len <= src_start) || + WARN_ON_ONCE(dst_start + len <= dst_start)) + goto out; + + /* + * Make sure the vma is not shared, that the src and dst remap + * ranges are both valid and fully within a single existing + * vma. + */ + src_vma = find_vma(mm, src_start); + if (!src_vma || (src_vma->vm_flags & VM_SHARED)) + goto out; + if (src_start < src_vma->vm_start || + src_start + len > src_vma->vm_end) + goto out; + + dst_vma = find_vma(mm, dst_start); + if (!dst_vma || (dst_vma->vm_flags & VM_SHARED)) + goto out; + if (dst_start < dst_vma->vm_start || + dst_start + len > dst_vma->vm_end) + goto out; + + err = validate_move_areas(ctx, src_vma, dst_vma); + if (err) + goto out; + + for (src_addr = src_start, dst_addr = dst_start; + src_addr < src_start + len;) { + spinlock_t *ptl; + pmd_t dst_pmdval; + unsigned long step_size; + + /* + * Below works because anonymous area would not have a + * transparent huge PUD. If file-backed support is added, + * that case would need to be handled here. + */ + src_pmd = mm_find_pmd(mm, src_addr); + if (unlikely(!src_pmd)) { + if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { + err = -ENOENT; + break; + } + src_pmd = mm_alloc_pmd(mm, src_addr); + if (unlikely(!src_pmd)) { + err = -ENOMEM; + break; + } + } + dst_pmd = mm_alloc_pmd(mm, dst_addr); + if (unlikely(!dst_pmd)) { + err = -ENOMEM; + break; + } + + dst_pmdval = pmdp_get_lockless(dst_pmd); + /* + * If the dst_pmd is mapped as THP don't override it and just + * be strict. If dst_pmd changes into TPH after this check, the + * move_pages_huge_pmd() will detect the change and retry + * while move_pages_pte() will detect the change and fail. + */ + if (unlikely(pmd_trans_huge(dst_pmdval))) { + err = -EEXIST; + break; + } + + ptl = pmd_trans_huge_lock(src_pmd, src_vma); + if (ptl) { + if (pmd_devmap(*src_pmd)) { + spin_unlock(ptl); + err = -ENOENT; + break; + } + + /* Check if we can move the pmd without splitting it. */ + if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || + !pmd_none(dst_pmdval)) { + struct folio *folio = pfn_folio(pmd_pfn(*src_pmd)); + + if (!folio || !PageAnonExclusive(&folio->page)) { + spin_unlock(ptl); + err = -EBUSY; + break; + } + + spin_unlock(ptl); + split_huge_pmd(src_vma, src_pmd, src_addr); + /* The folio will be split by move_pages_pte() */ + continue; + } + + err = move_pages_huge_pmd(mm, dst_pmd, src_pmd, + dst_pmdval, dst_vma, src_vma, + dst_addr, src_addr); + step_size = HPAGE_PMD_SIZE; + } else { + if (pmd_none(*src_pmd)) { + if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) { + err = -ENOENT; + break; + } + if (unlikely(__pte_alloc(mm, src_pmd))) { + err = -ENOMEM; + break; + } + } + + if (unlikely(pte_alloc(mm, dst_pmd))) { + err = -ENOMEM; + break; + } + + err = move_pages_pte(mm, dst_pmd, src_pmd, + dst_vma, src_vma, + dst_addr, src_addr, mode); + step_size = PAGE_SIZE; + } + + cond_resched(); + + if (fatal_signal_pending(current)) { + /* Do not override an error */ + if (!err || err == -EAGAIN) + err = -EINTR; + break; + } + + if (err) { + if (err == -EAGAIN) + continue; + break; + } + + /* Proceed to the next page */ + dst_addr += step_size; + src_addr += step_size; + moved += step_size; + } + +out: + VM_WARN_ON(moved < 0); + VM_WARN_ON(err > 0); + VM_WARN_ON(!moved && !err); + return moved ? moved : err; +} |