1 /* 2 * linux/mm/mlock.c 3 * 4 * (C) Copyright 1995 Linus Torvalds 5 * (C) Copyright 2002 Christoph Hellwig 6 */ 7 8 #include <linux/capability.h> 9 #include <linux/mman.h> 10 #include <linux/mm.h> 11 #include <linux/swap.h> 12 #include <linux/swapops.h> 13 #include <linux/pagemap.h> 14 #include <linux/mempolicy.h> 15 #include <linux/syscalls.h> 16 #include <linux/sched.h> 17 #include <linux/export.h> 18 #include <linux/rmap.h> 19 #include <linux/mmzone.h> 20 #include <linux/hugetlb.h> 21 22 #include "internal.h" 23 24 int can_do_mlock(void) 25 { 26 if (capable(CAP_IPC_LOCK)) 27 return 1; 28 if (rlimit(RLIMIT_MEMLOCK) != 0) 29 return 1; 30 return 0; 31 } 32 EXPORT_SYMBOL(can_do_mlock); 33 34 /* 35 * Mlocked pages are marked with PageMlocked() flag for efficient testing 36 * in vmscan and, possibly, the fault path; and to support semi-accurate 37 * statistics. 38 * 39 * An mlocked page [PageMlocked(page)] is unevictable. As such, it will 40 * be placed on the LRU "unevictable" list, rather than the [in]active lists. 41 * The unevictable list is an LRU sibling list to the [in]active lists. 42 * PageUnevictable is set to indicate the unevictable state. 43 * 44 * When lazy mlocking via vmscan, it is important to ensure that the 45 * vma's VM_LOCKED status is not concurrently being modified, otherwise we 46 * may have mlocked a page that is being munlocked. So lazy mlock must take 47 * the mmap_sem for read, and verify that the vma really is locked 48 * (see mm/rmap.c). 49 */ 50 51 /* 52 * LRU accounting for clear_page_mlock() 53 */ 54 void clear_page_mlock(struct page *page) 55 { 56 if (!TestClearPageMlocked(page)) 57 return; 58 59 mod_zone_page_state(page_zone(page), NR_MLOCK, 60 -hpage_nr_pages(page)); 61 count_vm_event(UNEVICTABLE_PGCLEARED); 62 if (!isolate_lru_page(page)) { 63 putback_lru_page(page); 64 } else { 65 /* 66 * We lost the race. the page already moved to evictable list. 67 */ 68 if (PageUnevictable(page)) 69 count_vm_event(UNEVICTABLE_PGSTRANDED); 70 } 71 } 72 73 /* 74 * Mark page as mlocked if not already. 75 * If page on LRU, isolate and putback to move to unevictable list. 76 */ 77 void mlock_vma_page(struct page *page) 78 { 79 BUG_ON(!PageLocked(page)); 80 81 if (!TestSetPageMlocked(page)) { 82 mod_zone_page_state(page_zone(page), NR_MLOCK, 83 hpage_nr_pages(page)); 84 count_vm_event(UNEVICTABLE_PGMLOCKED); 85 if (!isolate_lru_page(page)) 86 putback_lru_page(page); 87 } 88 } 89 90 /** 91 * munlock_vma_page - munlock a vma page 92 * @page - page to be unlocked 93 * 94 * called from munlock()/munmap() path with page supposedly on the LRU. 95 * When we munlock a page, because the vma where we found the page is being 96 * munlock()ed or munmap()ed, we want to check whether other vmas hold the 97 * page locked so that we can leave it on the unevictable lru list and not 98 * bother vmscan with it. However, to walk the page's rmap list in 99 * try_to_munlock() we must isolate the page from the LRU. If some other 100 * task has removed the page from the LRU, we won't be able to do that. 101 * So we clear the PageMlocked as we might not get another chance. If we 102 * can't isolate the page, we leave it for putback_lru_page() and vmscan 103 * [page_referenced()/try_to_unmap()] to deal with. 104 */ 105 void munlock_vma_page(struct page *page) 106 { 107 BUG_ON(!PageLocked(page)); 108 109 if (TestClearPageMlocked(page)) { 110 mod_zone_page_state(page_zone(page), NR_MLOCK, 111 -hpage_nr_pages(page)); 112 if (!isolate_lru_page(page)) { 113 int ret = SWAP_AGAIN; 114 115 /* 116 * Optimization: if the page was mapped just once, 117 * that's our mapping and we don't need to check all the 118 * other vmas. 119 */ 120 if (page_mapcount(page) > 1) 121 ret = try_to_munlock(page); 122 /* 123 * did try_to_unlock() succeed or punt? 124 */ 125 if (ret != SWAP_MLOCK) 126 count_vm_event(UNEVICTABLE_PGMUNLOCKED); 127 128 putback_lru_page(page); 129 } else { 130 /* 131 * Some other task has removed the page from the LRU. 132 * putback_lru_page() will take care of removing the 133 * page from the unevictable list, if necessary. 134 * vmscan [page_referenced()] will move the page back 135 * to the unevictable list if some other vma has it 136 * mlocked. 137 */ 138 if (PageUnevictable(page)) 139 count_vm_event(UNEVICTABLE_PGSTRANDED); 140 else 141 count_vm_event(UNEVICTABLE_PGMUNLOCKED); 142 } 143 } 144 } 145 146 /** 147 * __mlock_vma_pages_range() - mlock a range of pages in the vma. 148 * @vma: target vma 149 * @start: start address 150 * @end: end address 151 * 152 * This takes care of making the pages present too. 153 * 154 * return 0 on success, negative error code on error. 155 * 156 * vma->vm_mm->mmap_sem must be held for at least read. 157 */ 158 long __mlock_vma_pages_range(struct vm_area_struct *vma, 159 unsigned long start, unsigned long end, int *nonblocking) 160 { 161 struct mm_struct *mm = vma->vm_mm; 162 unsigned long addr = start; 163 int nr_pages = (end - start) / PAGE_SIZE; 164 int gup_flags; 165 166 VM_BUG_ON(start & ~PAGE_MASK); 167 VM_BUG_ON(end & ~PAGE_MASK); 168 VM_BUG_ON(start < vma->vm_start); 169 VM_BUG_ON(end > vma->vm_end); 170 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 171 172 gup_flags = FOLL_TOUCH | FOLL_MLOCK; 173 /* 174 * We want to touch writable mappings with a write fault in order 175 * to break COW, except for shared mappings because these don't COW 176 * and we would not want to dirty them for nothing. 177 */ 178 if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE) 179 gup_flags |= FOLL_WRITE; 180 181 /* 182 * We want mlock to succeed for regions that have any permissions 183 * other than PROT_NONE. 184 */ 185 if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) 186 gup_flags |= FOLL_FORCE; 187 188 return __get_user_pages(current, mm, addr, nr_pages, gup_flags, 189 NULL, NULL, nonblocking); 190 } 191 192 /* 193 * convert get_user_pages() return value to posix mlock() error 194 */ 195 static int __mlock_posix_error_return(long retval) 196 { 197 if (retval == -EFAULT) 198 retval = -ENOMEM; 199 else if (retval == -ENOMEM) 200 retval = -EAGAIN; 201 return retval; 202 } 203 204 /* 205 * munlock_vma_pages_range() - munlock all pages in the vma range.' 206 * @vma - vma containing range to be munlock()ed. 207 * @start - start address in @vma of the range 208 * @end - end of range in @vma. 209 * 210 * For mremap(), munmap() and exit(). 211 * 212 * Called with @vma VM_LOCKED. 213 * 214 * Returns with VM_LOCKED cleared. Callers must be prepared to 215 * deal with this. 216 * 217 * We don't save and restore VM_LOCKED here because pages are 218 * still on lru. In unmap path, pages might be scanned by reclaim 219 * and re-mlocked by try_to_{munlock|unmap} before we unmap and 220 * free them. This will result in freeing mlocked pages. 221 */ 222 void munlock_vma_pages_range(struct vm_area_struct *vma, 223 unsigned long start, unsigned long end) 224 { 225 unsigned long addr; 226 227 lru_add_drain(); 228 vma->vm_flags &= ~VM_LOCKED; 229 230 for (addr = start; addr < end; addr += PAGE_SIZE) { 231 struct page *page; 232 /* 233 * Although FOLL_DUMP is intended for get_dump_page(), 234 * it just so happens that its special treatment of the 235 * ZERO_PAGE (returning an error instead of doing get_page) 236 * suits munlock very well (and if somehow an abnormal page 237 * has sneaked into the range, we won't oops here: great). 238 */ 239 page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); 240 if (page && !IS_ERR(page)) { 241 lock_page(page); 242 munlock_vma_page(page); 243 unlock_page(page); 244 put_page(page); 245 } 246 cond_resched(); 247 } 248 } 249 250 /* 251 * mlock_fixup - handle mlock[all]/munlock[all] requests. 252 * 253 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and 254 * munlock is a no-op. However, for some special vmas, we go ahead and 255 * populate the ptes. 256 * 257 * For vmas that pass the filters, merge/split as appropriate. 258 */ 259 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, 260 unsigned long start, unsigned long end, vm_flags_t newflags) 261 { 262 struct mm_struct *mm = vma->vm_mm; 263 pgoff_t pgoff; 264 int nr_pages; 265 int ret = 0; 266 int lock = !!(newflags & VM_LOCKED); 267 268 if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) || 269 is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm)) 270 goto out; /* don't set VM_LOCKED, don't count */ 271 272 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); 273 *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma, 274 vma->vm_file, pgoff, vma_policy(vma)); 275 if (*prev) { 276 vma = *prev; 277 goto success; 278 } 279 280 if (start != vma->vm_start) { 281 ret = split_vma(mm, vma, start, 1); 282 if (ret) 283 goto out; 284 } 285 286 if (end != vma->vm_end) { 287 ret = split_vma(mm, vma, end, 0); 288 if (ret) 289 goto out; 290 } 291 292 success: 293 /* 294 * Keep track of amount of locked VM. 295 */ 296 nr_pages = (end - start) >> PAGE_SHIFT; 297 if (!lock) 298 nr_pages = -nr_pages; 299 mm->locked_vm += nr_pages; 300 301 /* 302 * vm_flags is protected by the mmap_sem held in write mode. 303 * It's okay if try_to_unmap_one unmaps a page just after we 304 * set VM_LOCKED, __mlock_vma_pages_range will bring it back. 305 */ 306 307 if (lock) 308 vma->vm_flags = newflags; 309 else 310 munlock_vma_pages_range(vma, start, end); 311 312 out: 313 *prev = vma; 314 return ret; 315 } 316 317 static int do_mlock(unsigned long start, size_t len, int on) 318 { 319 unsigned long nstart, end, tmp; 320 struct vm_area_struct * vma, * prev; 321 int error; 322 323 VM_BUG_ON(start & ~PAGE_MASK); 324 VM_BUG_ON(len != PAGE_ALIGN(len)); 325 end = start + len; 326 if (end < start) 327 return -EINVAL; 328 if (end == start) 329 return 0; 330 vma = find_vma(current->mm, start); 331 if (!vma || vma->vm_start > start) 332 return -ENOMEM; 333 334 prev = vma->vm_prev; 335 if (start > vma->vm_start) 336 prev = vma; 337 338 for (nstart = start ; ; ) { 339 vm_flags_t newflags; 340 341 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ 342 343 newflags = vma->vm_flags & ~VM_LOCKED; 344 if (on) 345 newflags |= VM_LOCKED | VM_POPULATE; 346 347 tmp = vma->vm_end; 348 if (tmp > end) 349 tmp = end; 350 error = mlock_fixup(vma, &prev, nstart, tmp, newflags); 351 if (error) 352 break; 353 nstart = tmp; 354 if (nstart < prev->vm_end) 355 nstart = prev->vm_end; 356 if (nstart >= end) 357 break; 358 359 vma = prev->vm_next; 360 if (!vma || vma->vm_start != nstart) { 361 error = -ENOMEM; 362 break; 363 } 364 } 365 return error; 366 } 367 368 /* 369 * __mm_populate - populate and/or mlock pages within a range of address space. 370 * 371 * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap 372 * flags. VMAs must be already marked with the desired vm_flags, and 373 * mmap_sem must not be held. 374 */ 375 int __mm_populate(unsigned long start, unsigned long len, int ignore_errors) 376 { 377 struct mm_struct *mm = current->mm; 378 unsigned long end, nstart, nend; 379 struct vm_area_struct *vma = NULL; 380 int locked = 0; 381 int ret = 0; 382 383 VM_BUG_ON(start & ~PAGE_MASK); 384 VM_BUG_ON(len != PAGE_ALIGN(len)); 385 end = start + len; 386 387 for (nstart = start; nstart < end; nstart = nend) { 388 /* 389 * We want to fault in pages for [nstart; end) address range. 390 * Find first corresponding VMA. 391 */ 392 if (!locked) { 393 locked = 1; 394 down_read(&mm->mmap_sem); 395 vma = find_vma(mm, nstart); 396 } else if (nstart >= vma->vm_end) 397 vma = vma->vm_next; 398 if (!vma || vma->vm_start >= end) 399 break; 400 /* 401 * Set [nstart; nend) to intersection of desired address 402 * range with the first VMA. Also, skip undesirable VMA types. 403 */ 404 nend = min(end, vma->vm_end); 405 if ((vma->vm_flags & (VM_IO | VM_PFNMAP | VM_POPULATE)) != 406 VM_POPULATE) 407 continue; 408 if (nstart < vma->vm_start) 409 nstart = vma->vm_start; 410 /* 411 * Now fault in a range of pages. __mlock_vma_pages_range() 412 * double checks the vma flags, so that it won't mlock pages 413 * if the vma was already munlocked. 414 */ 415 ret = __mlock_vma_pages_range(vma, nstart, nend, &locked); 416 if (ret < 0) { 417 if (ignore_errors) { 418 ret = 0; 419 continue; /* continue at next VMA */ 420 } 421 ret = __mlock_posix_error_return(ret); 422 break; 423 } 424 nend = nstart + ret * PAGE_SIZE; 425 ret = 0; 426 } 427 if (locked) 428 up_read(&mm->mmap_sem); 429 return ret; /* 0 or negative error code */ 430 } 431 432 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) 433 { 434 unsigned long locked; 435 unsigned long lock_limit; 436 int error = -ENOMEM; 437 438 if (!can_do_mlock()) 439 return -EPERM; 440 441 lru_add_drain_all(); /* flush pagevec */ 442 443 down_write(¤t->mm->mmap_sem); 444 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 445 start &= PAGE_MASK; 446 447 locked = len >> PAGE_SHIFT; 448 locked += current->mm->locked_vm; 449 450 lock_limit = rlimit(RLIMIT_MEMLOCK); 451 lock_limit >>= PAGE_SHIFT; 452 453 /* check against resource limits */ 454 if ((locked <= lock_limit) || capable(CAP_IPC_LOCK)) 455 error = do_mlock(start, len, 1); 456 up_write(¤t->mm->mmap_sem); 457 if (!error) 458 error = __mm_populate(start, len, 0); 459 return error; 460 } 461 462 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) 463 { 464 int ret; 465 466 down_write(¤t->mm->mmap_sem); 467 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 468 start &= PAGE_MASK; 469 ret = do_mlock(start, len, 0); 470 up_write(¤t->mm->mmap_sem); 471 return ret; 472 } 473 474 static int do_mlockall(int flags) 475 { 476 struct vm_area_struct * vma, * prev = NULL; 477 478 if (flags & MCL_FUTURE) 479 current->mm->def_flags |= VM_LOCKED | VM_POPULATE; 480 else 481 current->mm->def_flags &= ~(VM_LOCKED | VM_POPULATE); 482 if (flags == MCL_FUTURE) 483 goto out; 484 485 for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { 486 vm_flags_t newflags; 487 488 newflags = vma->vm_flags & ~VM_LOCKED; 489 if (flags & MCL_CURRENT) 490 newflags |= VM_LOCKED | VM_POPULATE; 491 492 /* Ignore errors */ 493 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); 494 } 495 out: 496 return 0; 497 } 498 499 SYSCALL_DEFINE1(mlockall, int, flags) 500 { 501 unsigned long lock_limit; 502 int ret = -EINVAL; 503 504 if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE))) 505 goto out; 506 507 ret = -EPERM; 508 if (!can_do_mlock()) 509 goto out; 510 511 if (flags & MCL_CURRENT) 512 lru_add_drain_all(); /* flush pagevec */ 513 514 down_write(¤t->mm->mmap_sem); 515 516 lock_limit = rlimit(RLIMIT_MEMLOCK); 517 lock_limit >>= PAGE_SHIFT; 518 519 ret = -ENOMEM; 520 if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) || 521 capable(CAP_IPC_LOCK)) 522 ret = do_mlockall(flags); 523 up_write(¤t->mm->mmap_sem); 524 if (!ret && (flags & MCL_CURRENT)) 525 mm_populate(0, TASK_SIZE); 526 out: 527 return ret; 528 } 529 530 SYSCALL_DEFINE0(munlockall) 531 { 532 int ret; 533 534 down_write(¤t->mm->mmap_sem); 535 ret = do_mlockall(0); 536 up_write(¤t->mm->mmap_sem); 537 return ret; 538 } 539 540 /* 541 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB 542 * shm segments) get accounted against the user_struct instead. 543 */ 544 static DEFINE_SPINLOCK(shmlock_user_lock); 545 546 int user_shm_lock(size_t size, struct user_struct *user) 547 { 548 unsigned long lock_limit, locked; 549 int allowed = 0; 550 551 locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 552 lock_limit = rlimit(RLIMIT_MEMLOCK); 553 if (lock_limit == RLIM_INFINITY) 554 allowed = 1; 555 lock_limit >>= PAGE_SHIFT; 556 spin_lock(&shmlock_user_lock); 557 if (!allowed && 558 locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK)) 559 goto out; 560 get_uid(user); 561 user->locked_shm += locked; 562 allowed = 1; 563 out: 564 spin_unlock(&shmlock_user_lock); 565 return allowed; 566 } 567 568 void user_shm_unlock(size_t size, struct user_struct *user) 569 { 570 spin_lock(&shmlock_user_lock); 571 user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 572 spin_unlock(&shmlock_user_lock); 573 free_uid(user); 574 } 575