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/module.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 VM_BUG_ON(!PageLocked(page)); 57 58 if (!page->mapping) { /* truncated ? */ 59 return; 60 } 61 62 dec_zone_page_state(page, NR_MLOCK); 63 count_vm_event(UNEVICTABLE_PGCLEARED); 64 if (!isolate_lru_page(page)) { 65 putback_lru_page(page); 66 } else { 67 /* 68 * We lost the race. the page already moved to evictable list. 69 */ 70 if (PageUnevictable(page)) 71 count_vm_event(UNEVICTABLE_PGSTRANDED); 72 } 73 } 74 75 /* 76 * Mark page as mlocked if not already. 77 * If page on LRU, isolate and putback to move to unevictable list. 78 */ 79 void mlock_vma_page(struct page *page) 80 { 81 BUG_ON(!PageLocked(page)); 82 83 if (!TestSetPageMlocked(page)) { 84 inc_zone_page_state(page, NR_MLOCK); 85 count_vm_event(UNEVICTABLE_PGMLOCKED); 86 if (!isolate_lru_page(page)) 87 putback_lru_page(page); 88 } 89 } 90 91 /** 92 * munlock_vma_page - munlock a vma page 93 * @page - page to be unlocked 94 * 95 * called from munlock()/munmap() path with page supposedly on the LRU. 96 * When we munlock a page, because the vma where we found the page is being 97 * munlock()ed or munmap()ed, we want to check whether other vmas hold the 98 * page locked so that we can leave it on the unevictable lru list and not 99 * bother vmscan with it. However, to walk the page's rmap list in 100 * try_to_munlock() we must isolate the page from the LRU. If some other 101 * task has removed the page from the LRU, we won't be able to do that. 102 * So we clear the PageMlocked as we might not get another chance. If we 103 * can't isolate the page, we leave it for putback_lru_page() and vmscan 104 * [page_referenced()/try_to_unmap()] to deal with. 105 */ 106 void munlock_vma_page(struct page *page) 107 { 108 BUG_ON(!PageLocked(page)); 109 110 if (TestClearPageMlocked(page)) { 111 dec_zone_page_state(page, NR_MLOCK); 112 if (!isolate_lru_page(page)) { 113 int ret = try_to_munlock(page); 114 /* 115 * did try_to_unlock() succeed or punt? 116 */ 117 if (ret != SWAP_MLOCK) 118 count_vm_event(UNEVICTABLE_PGMUNLOCKED); 119 120 putback_lru_page(page); 121 } else { 122 /* 123 * Some other task has removed the page from the LRU. 124 * putback_lru_page() will take care of removing the 125 * page from the unevictable list, if necessary. 126 * vmscan [page_referenced()] will move the page back 127 * to the unevictable list if some other vma has it 128 * mlocked. 129 */ 130 if (PageUnevictable(page)) 131 count_vm_event(UNEVICTABLE_PGSTRANDED); 132 else 133 count_vm_event(UNEVICTABLE_PGMUNLOCKED); 134 } 135 } 136 } 137 138 static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr) 139 { 140 return (vma->vm_flags & VM_GROWSDOWN) && 141 (vma->vm_start == addr) && 142 !vma_stack_continue(vma->vm_prev, addr); 143 } 144 145 /** 146 * __mlock_vma_pages_range() - mlock a range of pages in the vma. 147 * @vma: target vma 148 * @start: start address 149 * @end: end address 150 * 151 * This takes care of making the pages present too. 152 * 153 * return 0 on success, negative error code on error. 154 * 155 * vma->vm_mm->mmap_sem must be held for at least read. 156 */ 157 static long __mlock_vma_pages_range(struct vm_area_struct *vma, 158 unsigned long start, unsigned long end, 159 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; 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 if (vma->vm_flags & VM_LOCKED) 182 gup_flags |= FOLL_MLOCK; 183 184 /* We don't try to access the guard page of a stack vma */ 185 if (stack_guard_page(vma, start)) { 186 addr += PAGE_SIZE; 187 nr_pages--; 188 } 189 190 return __get_user_pages(current, mm, addr, nr_pages, gup_flags, 191 NULL, NULL, nonblocking); 192 } 193 194 /* 195 * convert get_user_pages() return value to posix mlock() error 196 */ 197 static int __mlock_posix_error_return(long retval) 198 { 199 if (retval == -EFAULT) 200 retval = -ENOMEM; 201 else if (retval == -ENOMEM) 202 retval = -EAGAIN; 203 return retval; 204 } 205 206 /** 207 * mlock_vma_pages_range() - mlock pages in specified vma range. 208 * @vma - the vma containing the specfied address range 209 * @start - starting address in @vma to mlock 210 * @end - end address [+1] in @vma to mlock 211 * 212 * For mmap()/mremap()/expansion of mlocked vma. 213 * 214 * return 0 on success for "normal" vmas. 215 * 216 * return number of pages [> 0] to be removed from locked_vm on success 217 * of "special" vmas. 218 */ 219 long mlock_vma_pages_range(struct vm_area_struct *vma, 220 unsigned long start, unsigned long end) 221 { 222 int nr_pages = (end - start) / PAGE_SIZE; 223 BUG_ON(!(vma->vm_flags & VM_LOCKED)); 224 225 /* 226 * filter unlockable vmas 227 */ 228 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 229 goto no_mlock; 230 231 if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || 232 is_vm_hugetlb_page(vma) || 233 vma == get_gate_vma(current))) { 234 235 __mlock_vma_pages_range(vma, start, end, NULL); 236 237 /* Hide errors from mmap() and other callers */ 238 return 0; 239 } 240 241 /* 242 * User mapped kernel pages or huge pages: 243 * make these pages present to populate the ptes, but 244 * fall thru' to reset VM_LOCKED--no need to unlock, and 245 * return nr_pages so these don't get counted against task's 246 * locked limit. huge pages are already counted against 247 * locked vm limit. 248 */ 249 make_pages_present(start, end); 250 251 no_mlock: 252 vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */ 253 return nr_pages; /* error or pages NOT mlocked */ 254 } 255 256 /* 257 * munlock_vma_pages_range() - munlock all pages in the vma range.' 258 * @vma - vma containing range to be munlock()ed. 259 * @start - start address in @vma of the range 260 * @end - end of range in @vma. 261 * 262 * For mremap(), munmap() and exit(). 263 * 264 * Called with @vma VM_LOCKED. 265 * 266 * Returns with VM_LOCKED cleared. Callers must be prepared to 267 * deal with this. 268 * 269 * We don't save and restore VM_LOCKED here because pages are 270 * still on lru. In unmap path, pages might be scanned by reclaim 271 * and re-mlocked by try_to_{munlock|unmap} before we unmap and 272 * free them. This will result in freeing mlocked pages. 273 */ 274 void munlock_vma_pages_range(struct vm_area_struct *vma, 275 unsigned long start, unsigned long end) 276 { 277 unsigned long addr; 278 279 lru_add_drain(); 280 vma->vm_flags &= ~VM_LOCKED; 281 282 for (addr = start; addr < end; addr += PAGE_SIZE) { 283 struct page *page; 284 /* 285 * Although FOLL_DUMP is intended for get_dump_page(), 286 * it just so happens that its special treatment of the 287 * ZERO_PAGE (returning an error instead of doing get_page) 288 * suits munlock very well (and if somehow an abnormal page 289 * has sneaked into the range, we won't oops here: great). 290 */ 291 page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); 292 if (page && !IS_ERR(page)) { 293 lock_page(page); 294 /* 295 * Like in __mlock_vma_pages_range(), 296 * because we lock page here and migration is 297 * blocked by the elevated reference, we need 298 * only check for file-cache page truncation. 299 */ 300 if (page->mapping) 301 munlock_vma_page(page); 302 unlock_page(page); 303 put_page(page); 304 } 305 cond_resched(); 306 } 307 } 308 309 /* 310 * mlock_fixup - handle mlock[all]/munlock[all] requests. 311 * 312 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and 313 * munlock is a no-op. However, for some special vmas, we go ahead and 314 * populate the ptes via make_pages_present(). 315 * 316 * For vmas that pass the filters, merge/split as appropriate. 317 */ 318 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, 319 unsigned long start, unsigned long end, unsigned int newflags) 320 { 321 struct mm_struct *mm = vma->vm_mm; 322 pgoff_t pgoff; 323 int nr_pages; 324 int ret = 0; 325 int lock = newflags & VM_LOCKED; 326 327 if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) || 328 is_vm_hugetlb_page(vma) || vma == get_gate_vma(current)) 329 goto out; /* don't set VM_LOCKED, don't count */ 330 331 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); 332 *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma, 333 vma->vm_file, pgoff, vma_policy(vma)); 334 if (*prev) { 335 vma = *prev; 336 goto success; 337 } 338 339 if (start != vma->vm_start) { 340 ret = split_vma(mm, vma, start, 1); 341 if (ret) 342 goto out; 343 } 344 345 if (end != vma->vm_end) { 346 ret = split_vma(mm, vma, end, 0); 347 if (ret) 348 goto out; 349 } 350 351 success: 352 /* 353 * Keep track of amount of locked VM. 354 */ 355 nr_pages = (end - start) >> PAGE_SHIFT; 356 if (!lock) 357 nr_pages = -nr_pages; 358 mm->locked_vm += nr_pages; 359 360 /* 361 * vm_flags is protected by the mmap_sem held in write mode. 362 * It's okay if try_to_unmap_one unmaps a page just after we 363 * set VM_LOCKED, __mlock_vma_pages_range will bring it back. 364 */ 365 366 if (lock) 367 vma->vm_flags = newflags; 368 else 369 munlock_vma_pages_range(vma, start, end); 370 371 out: 372 *prev = vma; 373 return ret; 374 } 375 376 static int do_mlock(unsigned long start, size_t len, int on) 377 { 378 unsigned long nstart, end, tmp; 379 struct vm_area_struct * vma, * prev; 380 int error; 381 382 VM_BUG_ON(start & ~PAGE_MASK); 383 VM_BUG_ON(len != PAGE_ALIGN(len)); 384 end = start + len; 385 if (end < start) 386 return -EINVAL; 387 if (end == start) 388 return 0; 389 vma = find_vma_prev(current->mm, start, &prev); 390 if (!vma || vma->vm_start > start) 391 return -ENOMEM; 392 393 if (start > vma->vm_start) 394 prev = vma; 395 396 for (nstart = start ; ; ) { 397 unsigned int newflags; 398 399 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ 400 401 newflags = vma->vm_flags | VM_LOCKED; 402 if (!on) 403 newflags &= ~VM_LOCKED; 404 405 tmp = vma->vm_end; 406 if (tmp > end) 407 tmp = end; 408 error = mlock_fixup(vma, &prev, nstart, tmp, newflags); 409 if (error) 410 break; 411 nstart = tmp; 412 if (nstart < prev->vm_end) 413 nstart = prev->vm_end; 414 if (nstart >= end) 415 break; 416 417 vma = prev->vm_next; 418 if (!vma || vma->vm_start != nstart) { 419 error = -ENOMEM; 420 break; 421 } 422 } 423 return error; 424 } 425 426 static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors) 427 { 428 struct mm_struct *mm = current->mm; 429 unsigned long end, nstart, nend; 430 struct vm_area_struct *vma = NULL; 431 int locked = 0; 432 int ret = 0; 433 434 VM_BUG_ON(start & ~PAGE_MASK); 435 VM_BUG_ON(len != PAGE_ALIGN(len)); 436 end = start + len; 437 438 for (nstart = start; nstart < end; nstart = nend) { 439 /* 440 * We want to fault in pages for [nstart; end) address range. 441 * Find first corresponding VMA. 442 */ 443 if (!locked) { 444 locked = 1; 445 down_read(&mm->mmap_sem); 446 vma = find_vma(mm, nstart); 447 } else if (nstart >= vma->vm_end) 448 vma = vma->vm_next; 449 if (!vma || vma->vm_start >= end) 450 break; 451 /* 452 * Set [nstart; nend) to intersection of desired address 453 * range with the first VMA. Also, skip undesirable VMA types. 454 */ 455 nend = min(end, vma->vm_end); 456 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 457 continue; 458 if (nstart < vma->vm_start) 459 nstart = vma->vm_start; 460 /* 461 * Now fault in a range of pages. __mlock_vma_pages_range() 462 * double checks the vma flags, so that it won't mlock pages 463 * if the vma was already munlocked. 464 */ 465 ret = __mlock_vma_pages_range(vma, nstart, nend, &locked); 466 if (ret < 0) { 467 if (ignore_errors) { 468 ret = 0; 469 continue; /* continue at next VMA */ 470 } 471 ret = __mlock_posix_error_return(ret); 472 break; 473 } 474 nend = nstart + ret * PAGE_SIZE; 475 ret = 0; 476 } 477 if (locked) 478 up_read(&mm->mmap_sem); 479 return ret; /* 0 or negative error code */ 480 } 481 482 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) 483 { 484 unsigned long locked; 485 unsigned long lock_limit; 486 int error = -ENOMEM; 487 488 if (!can_do_mlock()) 489 return -EPERM; 490 491 lru_add_drain_all(); /* flush pagevec */ 492 493 down_write(¤t->mm->mmap_sem); 494 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 495 start &= PAGE_MASK; 496 497 locked = len >> PAGE_SHIFT; 498 locked += current->mm->locked_vm; 499 500 lock_limit = rlimit(RLIMIT_MEMLOCK); 501 lock_limit >>= PAGE_SHIFT; 502 503 /* check against resource limits */ 504 if ((locked <= lock_limit) || capable(CAP_IPC_LOCK)) 505 error = do_mlock(start, len, 1); 506 up_write(¤t->mm->mmap_sem); 507 if (!error) 508 error = do_mlock_pages(start, len, 0); 509 return error; 510 } 511 512 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) 513 { 514 int ret; 515 516 down_write(¤t->mm->mmap_sem); 517 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 518 start &= PAGE_MASK; 519 ret = do_mlock(start, len, 0); 520 up_write(¤t->mm->mmap_sem); 521 return ret; 522 } 523 524 static int do_mlockall(int flags) 525 { 526 struct vm_area_struct * vma, * prev = NULL; 527 unsigned int def_flags = 0; 528 529 if (flags & MCL_FUTURE) 530 def_flags = VM_LOCKED; 531 current->mm->def_flags = def_flags; 532 if (flags == MCL_FUTURE) 533 goto out; 534 535 for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { 536 unsigned int newflags; 537 538 newflags = vma->vm_flags | VM_LOCKED; 539 if (!(flags & MCL_CURRENT)) 540 newflags &= ~VM_LOCKED; 541 542 /* Ignore errors */ 543 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); 544 } 545 out: 546 return 0; 547 } 548 549 SYSCALL_DEFINE1(mlockall, int, flags) 550 { 551 unsigned long lock_limit; 552 int ret = -EINVAL; 553 554 if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE))) 555 goto out; 556 557 ret = -EPERM; 558 if (!can_do_mlock()) 559 goto out; 560 561 lru_add_drain_all(); /* flush pagevec */ 562 563 down_write(¤t->mm->mmap_sem); 564 565 lock_limit = rlimit(RLIMIT_MEMLOCK); 566 lock_limit >>= PAGE_SHIFT; 567 568 ret = -ENOMEM; 569 if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) || 570 capable(CAP_IPC_LOCK)) 571 ret = do_mlockall(flags); 572 up_write(¤t->mm->mmap_sem); 573 if (!ret && (flags & MCL_CURRENT)) { 574 /* Ignore errors */ 575 do_mlock_pages(0, TASK_SIZE, 1); 576 } 577 out: 578 return ret; 579 } 580 581 SYSCALL_DEFINE0(munlockall) 582 { 583 int ret; 584 585 down_write(¤t->mm->mmap_sem); 586 ret = do_mlockall(0); 587 up_write(¤t->mm->mmap_sem); 588 return ret; 589 } 590 591 /* 592 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB 593 * shm segments) get accounted against the user_struct instead. 594 */ 595 static DEFINE_SPINLOCK(shmlock_user_lock); 596 597 int user_shm_lock(size_t size, struct user_struct *user) 598 { 599 unsigned long lock_limit, locked; 600 int allowed = 0; 601 602 locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 603 lock_limit = rlimit(RLIMIT_MEMLOCK); 604 if (lock_limit == RLIM_INFINITY) 605 allowed = 1; 606 lock_limit >>= PAGE_SHIFT; 607 spin_lock(&shmlock_user_lock); 608 if (!allowed && 609 locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK)) 610 goto out; 611 get_uid(user); 612 user->locked_shm += locked; 613 allowed = 1; 614 out: 615 spin_unlock(&shmlock_user_lock); 616 return allowed; 617 } 618 619 void user_shm_unlock(size_t size, struct user_struct *user) 620 { 621 spin_lock(&shmlock_user_lock); 622 user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 623 spin_unlock(&shmlock_user_lock); 624 free_uid(user); 625 } 626