| 1 | /* |
| 2 | * linux/mm/fremap.c |
| 3 | * |
| 4 | * Explicit pagetable population and nonlinear (random) mappings support. |
| 5 | * |
| 6 | * started by Ingo Molnar, Copyright (C) 2002, 2003 |
| 7 | */ |
| 8 | #include <linux/backing-dev.h> |
| 9 | #include <linux/mm.h> |
| 10 | #include <linux/swap.h> |
| 11 | #include <linux/file.h> |
| 12 | #include <linux/mman.h> |
| 13 | #include <linux/pagemap.h> |
| 14 | #include <linux/swapops.h> |
| 15 | #include <linux/rmap.h> |
| 16 | #include <linux/module.h> |
| 17 | #include <linux/syscalls.h> |
| 18 | |
| 19 | #include <asm/mmu_context.h> |
| 20 | #include <asm/cacheflush.h> |
| 21 | #include <asm/tlbflush.h> |
| 22 | |
| 23 | static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma, |
| 24 | unsigned long addr, pte_t *ptep) |
| 25 | { |
| 26 | pte_t pte = *ptep; |
| 27 | |
| 28 | if (pte_present(pte)) { |
| 29 | struct page *page; |
| 30 | |
| 31 | flush_cache_page(vma, addr, pte_pfn(pte)); |
| 32 | pte = ptep_clear_flush(vma, addr, ptep); |
| 33 | page = vm_normal_page(vma, addr, pte); |
| 34 | if (page) { |
| 35 | if (pte_dirty(pte)) |
| 36 | set_page_dirty(page); |
| 37 | page_remove_rmap(page, vma); |
| 38 | page_cache_release(page); |
| 39 | update_hiwater_rss(mm); |
| 40 | dec_mm_counter(mm, file_rss); |
| 41 | } |
| 42 | } else { |
| 43 | if (!pte_file(pte)) |
| 44 | free_swap_and_cache(pte_to_swp_entry(pte)); |
| 45 | pte_clear_not_present_full(mm, addr, ptep, 0); |
| 46 | } |
| 47 | } |
| 48 | |
| 49 | /* |
| 50 | * Install a file pte to a given virtual memory address, release any |
| 51 | * previously existing mapping. |
| 52 | */ |
| 53 | static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma, |
| 54 | unsigned long addr, unsigned long pgoff, pgprot_t prot) |
| 55 | { |
| 56 | int err = -ENOMEM; |
| 57 | pte_t *pte; |
| 58 | spinlock_t *ptl; |
| 59 | |
| 60 | pte = get_locked_pte(mm, addr, &ptl); |
| 61 | if (!pte) |
| 62 | goto out; |
| 63 | |
| 64 | if (!pte_none(*pte)) |
| 65 | zap_pte(mm, vma, addr, pte); |
| 66 | |
| 67 | set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff)); |
| 68 | /* |
| 69 | * We don't need to run update_mmu_cache() here because the "file pte" |
| 70 | * being installed by install_file_pte() is not a real pte - it's a |
| 71 | * non-present entry (like a swap entry), noting what file offset should |
| 72 | * be mapped there when there's a fault (in a non-linear vma where |
| 73 | * that's not obvious). |
| 74 | */ |
| 75 | pte_unmap_unlock(pte, ptl); |
| 76 | err = 0; |
| 77 | out: |
| 78 | return err; |
| 79 | } |
| 80 | |
| 81 | static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma, |
| 82 | unsigned long addr, unsigned long size, pgoff_t pgoff) |
| 83 | { |
| 84 | int err; |
| 85 | |
| 86 | do { |
| 87 | err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot); |
| 88 | if (err) |
| 89 | return err; |
| 90 | |
| 91 | size -= PAGE_SIZE; |
| 92 | addr += PAGE_SIZE; |
| 93 | pgoff++; |
| 94 | } while (size); |
| 95 | |
| 96 | return 0; |
| 97 | |
| 98 | } |
| 99 | |
| 100 | /** |
| 101 | * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma |
| 102 | * @start: start of the remapped virtual memory range |
| 103 | * @size: size of the remapped virtual memory range |
| 104 | * @prot: new protection bits of the range (see NOTE) |
| 105 | * @pgoff: to-be-mapped page of the backing store file |
| 106 | * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO. |
| 107 | * |
| 108 | * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma |
| 109 | * (shared backing store file). |
| 110 | * |
| 111 | * This syscall works purely via pagetables, so it's the most efficient |
| 112 | * way to map the same (large) file into a given virtual window. Unlike |
| 113 | * mmap()/mremap() it does not create any new vmas. The new mappings are |
| 114 | * also safe across swapout. |
| 115 | * |
| 116 | * NOTE: the @prot parameter right now is ignored (but must be zero), |
| 117 | * and the vma's default protection is used. Arbitrary protections |
| 118 | * might be implemented in the future. |
| 119 | */ |
| 120 | asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size, |
| 121 | unsigned long prot, unsigned long pgoff, unsigned long flags) |
| 122 | { |
| 123 | struct mm_struct *mm = current->mm; |
| 124 | struct address_space *mapping; |
| 125 | unsigned long end = start + size; |
| 126 | struct vm_area_struct *vma; |
| 127 | int err = -EINVAL; |
| 128 | int has_write_lock = 0; |
| 129 | |
| 130 | if (prot) |
| 131 | return err; |
| 132 | /* |
| 133 | * Sanitize the syscall parameters: |
| 134 | */ |
| 135 | start = start & PAGE_MASK; |
| 136 | size = size & PAGE_MASK; |
| 137 | |
| 138 | /* Does the address range wrap, or is the span zero-sized? */ |
| 139 | if (start + size <= start) |
| 140 | return err; |
| 141 | |
| 142 | /* Can we represent this offset inside this architecture's pte's? */ |
| 143 | #if PTE_FILE_MAX_BITS < BITS_PER_LONG |
| 144 | if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS)) |
| 145 | return err; |
| 146 | #endif |
| 147 | |
| 148 | /* We need down_write() to change vma->vm_flags. */ |
| 149 | down_read(&mm->mmap_sem); |
| 150 | retry: |
| 151 | vma = find_vma(mm, start); |
| 152 | |
| 153 | /* |
| 154 | * Make sure the vma is shared, that it supports prefaulting, |
| 155 | * and that the remapped range is valid and fully within |
| 156 | * the single existing vma. vm_private_data is used as a |
| 157 | * swapout cursor in a VM_NONLINEAR vma. |
| 158 | */ |
| 159 | if (!vma || !(vma->vm_flags & VM_SHARED)) |
| 160 | goto out; |
| 161 | |
| 162 | if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR)) |
| 163 | goto out; |
| 164 | |
| 165 | if (!(vma->vm_flags & VM_CAN_NONLINEAR)) |
| 166 | goto out; |
| 167 | |
| 168 | if (end <= start || start < vma->vm_start || end > vma->vm_end) |
| 169 | goto out; |
| 170 | |
| 171 | /* Must set VM_NONLINEAR before any pages are populated. */ |
| 172 | if (!(vma->vm_flags & VM_NONLINEAR)) { |
| 173 | /* Don't need a nonlinear mapping, exit success */ |
| 174 | if (pgoff == linear_page_index(vma, start)) { |
| 175 | err = 0; |
| 176 | goto out; |
| 177 | } |
| 178 | |
| 179 | if (!has_write_lock) { |
| 180 | up_read(&mm->mmap_sem); |
| 181 | down_write(&mm->mmap_sem); |
| 182 | has_write_lock = 1; |
| 183 | goto retry; |
| 184 | } |
| 185 | mapping = vma->vm_file->f_mapping; |
| 186 | /* |
| 187 | * page_mkclean doesn't work on nonlinear vmas, so if |
| 188 | * dirty pages need to be accounted, emulate with linear |
| 189 | * vmas. |
| 190 | */ |
| 191 | if (mapping_cap_account_dirty(mapping)) { |
| 192 | unsigned long addr; |
| 193 | struct file *file = vma->vm_file; |
| 194 | |
| 195 | flags &= MAP_NONBLOCK; |
| 196 | get_file(file); |
| 197 | addr = mmap_region(file, start, size, |
| 198 | flags, vma->vm_flags, pgoff, 1); |
| 199 | fput(file); |
| 200 | if (IS_ERR_VALUE(addr)) { |
| 201 | err = addr; |
| 202 | } else { |
| 203 | BUG_ON(addr != start); |
| 204 | err = 0; |
| 205 | } |
| 206 | goto out; |
| 207 | } |
| 208 | spin_lock(&mapping->i_mmap_lock); |
| 209 | flush_dcache_mmap_lock(mapping); |
| 210 | vma->vm_flags |= VM_NONLINEAR; |
| 211 | vma_prio_tree_remove(vma, &mapping->i_mmap); |
| 212 | vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear); |
| 213 | flush_dcache_mmap_unlock(mapping); |
| 214 | spin_unlock(&mapping->i_mmap_lock); |
| 215 | } |
| 216 | |
| 217 | err = populate_range(mm, vma, start, size, pgoff); |
| 218 | if (!err && !(flags & MAP_NONBLOCK)) { |
| 219 | if (unlikely(has_write_lock)) { |
| 220 | downgrade_write(&mm->mmap_sem); |
| 221 | has_write_lock = 0; |
| 222 | } |
| 223 | make_pages_present(start, start+size); |
| 224 | } |
| 225 | |
| 226 | /* |
| 227 | * We can't clear VM_NONLINEAR because we'd have to do |
| 228 | * it after ->populate completes, and that would prevent |
| 229 | * downgrading the lock. (Locks can't be upgraded). |
| 230 | */ |
| 231 | |
| 232 | out: |
| 233 | if (likely(!has_write_lock)) |
| 234 | up_read(&mm->mmap_sem); |
| 235 | else |
| 236 | up_write(&mm->mmap_sem); |
| 237 | |
| 238 | return err; |
| 239 | } |
| 240 | |