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 /* 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 if (vma->vm_flags & VM_LOCKED) 189 gup_flags |= FOLL_MLOCK; 190 191 /* We don't try to access the guard page of a stack vma */ 192 if (stack_guard_page(vma, start)) { 193 addr += PAGE_SIZE; 194 nr_pages--; 195 } 196 197 return __get_user_pages(current, mm, addr, nr_pages, gup_flags, 198 NULL, NULL, nonblocking); 199 } 200 201 /* 202 * convert get_user_pages() return value to posix mlock() error 203 */ 204 static int __mlock_posix_error_return(long retval) 205 { 206 if (retval == -EFAULT) 207 retval = -ENOMEM; 208 else if (retval == -ENOMEM) 209 retval = -EAGAIN; 210 return retval; 211 } 212 213 /** 214 * mlock_vma_pages_range() - mlock pages in specified vma range. 215 * @vma - the vma containing the specfied address range 216 * @start - starting address in @vma to mlock 217 * @end - end address [+1] in @vma to mlock 218 * 219 * For mmap()/mremap()/expansion of mlocked vma. 220 * 221 * return 0 on success for "normal" vmas. 222 * 223 * return number of pages [> 0] to be removed from locked_vm on success 224 * of "special" vmas. 225 */ 226 long mlock_vma_pages_range(struct vm_area_struct *vma, 227 unsigned long start, unsigned long end) 228 { 229 int nr_pages = (end - start) / PAGE_SIZE; 230 BUG_ON(!(vma->vm_flags & VM_LOCKED)); 231 232 /* 233 * filter unlockable vmas 234 */ 235 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 236 goto no_mlock; 237 238 if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || 239 is_vm_hugetlb_page(vma) || 240 vma == get_gate_vma(current))) { 241 242 __mlock_vma_pages_range(vma, start, end, NULL); 243 244 /* Hide errors from mmap() and other callers */ 245 return 0; 246 } 247 248 /* 249 * User mapped kernel pages or huge pages: 250 * make these pages present to populate the ptes, but 251 * fall thru' to reset VM_LOCKED--no need to unlock, and 252 * return nr_pages so these don't get counted against task's 253 * locked limit. huge pages are already counted against 254 * locked vm limit. 255 */ 256 make_pages_present(start, end); 257 258 no_mlock: 259 vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */ 260 return nr_pages; /* error or pages NOT mlocked */ 261 } 262 263 /* 264 * munlock_vma_pages_range() - munlock all pages in the vma range.' 265 * @vma - vma containing range to be munlock()ed. 266 * @start - start address in @vma of the range 267 * @end - end of range in @vma. 268 * 269 * For mremap(), munmap() and exit(). 270 * 271 * Called with @vma VM_LOCKED. 272 * 273 * Returns with VM_LOCKED cleared. Callers must be prepared to 274 * deal with this. 275 * 276 * We don't save and restore VM_LOCKED here because pages are 277 * still on lru. In unmap path, pages might be scanned by reclaim 278 * and re-mlocked by try_to_{munlock|unmap} before we unmap and 279 * free them. This will result in freeing mlocked pages. 280 */ 281 void munlock_vma_pages_range(struct vm_area_struct *vma, 282 unsigned long start, unsigned long end) 283 { 284 unsigned long addr; 285 286 lru_add_drain(); 287 vma->vm_flags &= ~VM_LOCKED; 288 289 for (addr = start; addr < end; addr += PAGE_SIZE) { 290 struct page *page; 291 /* 292 * Although FOLL_DUMP is intended for get_dump_page(), 293 * it just so happens that its special treatment of the 294 * ZERO_PAGE (returning an error instead of doing get_page) 295 * suits munlock very well (and if somehow an abnormal page 296 * has sneaked into the range, we won't oops here: great). 297 */ 298 page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); 299 if (page && !IS_ERR(page)) { 300 lock_page(page); 301 /* 302 * Like in __mlock_vma_pages_range(), 303 * because we lock page here and migration is 304 * blocked by the elevated reference, we need 305 * only check for file-cache page truncation. 306 */ 307 if (page->mapping) 308 munlock_vma_page(page); 309 unlock_page(page); 310 put_page(page); 311 } 312 cond_resched(); 313 } 314 } 315 316 /* 317 * mlock_fixup - handle mlock[all]/munlock[all] requests. 318 * 319 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and 320 * munlock is a no-op. However, for some special vmas, we go ahead and 321 * populate the ptes via make_pages_present(). 322 * 323 * For vmas that pass the filters, merge/split as appropriate. 324 */ 325 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, 326 unsigned long start, unsigned long end, unsigned int newflags) 327 { 328 struct mm_struct *mm = vma->vm_mm; 329 pgoff_t pgoff; 330 int nr_pages; 331 int ret = 0; 332 int lock = newflags & VM_LOCKED; 333 334 if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) || 335 is_vm_hugetlb_page(vma) || vma == get_gate_vma(current)) 336 goto out; /* don't set VM_LOCKED, don't count */ 337 338 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); 339 *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma, 340 vma->vm_file, pgoff, vma_policy(vma)); 341 if (*prev) { 342 vma = *prev; 343 goto success; 344 } 345 346 if (start != vma->vm_start) { 347 ret = split_vma(mm, vma, start, 1); 348 if (ret) 349 goto out; 350 } 351 352 if (end != vma->vm_end) { 353 ret = split_vma(mm, vma, end, 0); 354 if (ret) 355 goto out; 356 } 357 358 success: 359 /* 360 * Keep track of amount of locked VM. 361 */ 362 nr_pages = (end - start) >> PAGE_SHIFT; 363 if (!lock) 364 nr_pages = -nr_pages; 365 mm->locked_vm += nr_pages; 366 367 /* 368 * vm_flags is protected by the mmap_sem held in write mode. 369 * It's okay if try_to_unmap_one unmaps a page just after we 370 * set VM_LOCKED, __mlock_vma_pages_range will bring it back. 371 */ 372 373 if (lock) 374 vma->vm_flags = newflags; 375 else 376 munlock_vma_pages_range(vma, start, end); 377 378 out: 379 *prev = vma; 380 return ret; 381 } 382 383 static int do_mlock(unsigned long start, size_t len, int on) 384 { 385 unsigned long nstart, end, tmp; 386 struct vm_area_struct * vma, * prev; 387 int error; 388 389 VM_BUG_ON(start & ~PAGE_MASK); 390 VM_BUG_ON(len != PAGE_ALIGN(len)); 391 end = start + len; 392 if (end < start) 393 return -EINVAL; 394 if (end == start) 395 return 0; 396 vma = find_vma_prev(current->mm, start, &prev); 397 if (!vma || vma->vm_start > start) 398 return -ENOMEM; 399 400 if (start > vma->vm_start) 401 prev = vma; 402 403 for (nstart = start ; ; ) { 404 unsigned int newflags; 405 406 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ 407 408 newflags = vma->vm_flags | VM_LOCKED; 409 if (!on) 410 newflags &= ~VM_LOCKED; 411 412 tmp = vma->vm_end; 413 if (tmp > end) 414 tmp = end; 415 error = mlock_fixup(vma, &prev, nstart, tmp, newflags); 416 if (error) 417 break; 418 nstart = tmp; 419 if (nstart < prev->vm_end) 420 nstart = prev->vm_end; 421 if (nstart >= end) 422 break; 423 424 vma = prev->vm_next; 425 if (!vma || vma->vm_start != nstart) { 426 error = -ENOMEM; 427 break; 428 } 429 } 430 return error; 431 } 432 433 static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors) 434 { 435 struct mm_struct *mm = current->mm; 436 unsigned long end, nstart, nend; 437 struct vm_area_struct *vma = NULL; 438 int locked = 0; 439 int ret = 0; 440 441 VM_BUG_ON(start & ~PAGE_MASK); 442 VM_BUG_ON(len != PAGE_ALIGN(len)); 443 end = start + len; 444 445 for (nstart = start; nstart < end; nstart = nend) { 446 /* 447 * We want to fault in pages for [nstart; end) address range. 448 * Find first corresponding VMA. 449 */ 450 if (!locked) { 451 locked = 1; 452 down_read(&mm->mmap_sem); 453 vma = find_vma(mm, nstart); 454 } else if (nstart >= vma->vm_end) 455 vma = vma->vm_next; 456 if (!vma || vma->vm_start >= end) 457 break; 458 /* 459 * Set [nstart; nend) to intersection of desired address 460 * range with the first VMA. Also, skip undesirable VMA types. 461 */ 462 nend = min(end, vma->vm_end); 463 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 464 continue; 465 if (nstart < vma->vm_start) 466 nstart = vma->vm_start; 467 /* 468 * Now fault in a range of pages. __mlock_vma_pages_range() 469 * double checks the vma flags, so that it won't mlock pages 470 * if the vma was already munlocked. 471 */ 472 ret = __mlock_vma_pages_range(vma, nstart, nend, &locked); 473 if (ret < 0) { 474 if (ignore_errors) { 475 ret = 0; 476 continue; /* continue at next VMA */ 477 } 478 ret = __mlock_posix_error_return(ret); 479 break; 480 } 481 nend = nstart + ret * PAGE_SIZE; 482 ret = 0; 483 } 484 if (locked) 485 up_read(&mm->mmap_sem); 486 return ret; /* 0 or negative error code */ 487 } 488 489 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) 490 { 491 unsigned long locked; 492 unsigned long lock_limit; 493 int error = -ENOMEM; 494 495 if (!can_do_mlock()) 496 return -EPERM; 497 498 lru_add_drain_all(); /* flush pagevec */ 499 500 down_write(¤t->mm->mmap_sem); 501 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 502 start &= PAGE_MASK; 503 504 locked = len >> PAGE_SHIFT; 505 locked += current->mm->locked_vm; 506 507 lock_limit = rlimit(RLIMIT_MEMLOCK); 508 lock_limit >>= PAGE_SHIFT; 509 510 /* check against resource limits */ 511 if ((locked <= lock_limit) || capable(CAP_IPC_LOCK)) 512 error = do_mlock(start, len, 1); 513 up_write(¤t->mm->mmap_sem); 514 if (!error) 515 error = do_mlock_pages(start, len, 0); 516 return error; 517 } 518 519 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) 520 { 521 int ret; 522 523 down_write(¤t->mm->mmap_sem); 524 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 525 start &= PAGE_MASK; 526 ret = do_mlock(start, len, 0); 527 up_write(¤t->mm->mmap_sem); 528 return ret; 529 } 530 531 static int do_mlockall(int flags) 532 { 533 struct vm_area_struct * vma, * prev = NULL; 534 unsigned int def_flags = 0; 535 536 if (flags & MCL_FUTURE) 537 def_flags = VM_LOCKED; 538 current->mm->def_flags = def_flags; 539 if (flags == MCL_FUTURE) 540 goto out; 541 542 for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { 543 unsigned int newflags; 544 545 newflags = vma->vm_flags | VM_LOCKED; 546 if (!(flags & MCL_CURRENT)) 547 newflags &= ~VM_LOCKED; 548 549 /* Ignore errors */ 550 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); 551 } 552 out: 553 return 0; 554 } 555 556 SYSCALL_DEFINE1(mlockall, int, flags) 557 { 558 unsigned long lock_limit; 559 int ret = -EINVAL; 560 561 if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE))) 562 goto out; 563 564 ret = -EPERM; 565 if (!can_do_mlock()) 566 goto out; 567 568 lru_add_drain_all(); /* flush pagevec */ 569 570 down_write(¤t->mm->mmap_sem); 571 572 lock_limit = rlimit(RLIMIT_MEMLOCK); 573 lock_limit >>= PAGE_SHIFT; 574 575 ret = -ENOMEM; 576 if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) || 577 capable(CAP_IPC_LOCK)) 578 ret = do_mlockall(flags); 579 up_write(¤t->mm->mmap_sem); 580 if (!ret && (flags & MCL_CURRENT)) { 581 /* Ignore errors */ 582 do_mlock_pages(0, TASK_SIZE, 1); 583 } 584 out: 585 return ret; 586 } 587 588 SYSCALL_DEFINE0(munlockall) 589 { 590 int ret; 591 592 down_write(¤t->mm->mmap_sem); 593 ret = do_mlockall(0); 594 up_write(¤t->mm->mmap_sem); 595 return ret; 596 } 597 598 /* 599 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB 600 * shm segments) get accounted against the user_struct instead. 601 */ 602 static DEFINE_SPINLOCK(shmlock_user_lock); 603 604 int user_shm_lock(size_t size, struct user_struct *user) 605 { 606 unsigned long lock_limit, locked; 607 int allowed = 0; 608 609 locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 610 lock_limit = rlimit(RLIMIT_MEMLOCK); 611 if (lock_limit == RLIM_INFINITY) 612 allowed = 1; 613 lock_limit >>= PAGE_SHIFT; 614 spin_lock(&shmlock_user_lock); 615 if (!allowed && 616 locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK)) 617 goto out; 618 get_uid(user); 619 user->locked_shm += locked; 620 allowed = 1; 621 out: 622 spin_unlock(&shmlock_user_lock); 623 return allowed; 624 } 625 626 void user_shm_unlock(size_t size, struct user_struct *user) 627 { 628 spin_lock(&shmlock_user_lock); 629 user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 630 spin_unlock(&shmlock_user_lock); 631 free_uid(user); 632 } 633