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 /** 139 * __mlock_vma_pages_range() - mlock a range of pages in the vma. 140 * @vma: target vma 141 * @start: start address 142 * @end: end address 143 * 144 * This takes care of making the pages present too. 145 * 146 * return 0 on success, negative error code on error. 147 * 148 * vma->vm_mm->mmap_sem must be held for at least read. 149 */ 150 static long __mlock_vma_pages_range(struct vm_area_struct *vma, 151 unsigned long start, unsigned long end, 152 int *nonblocking) 153 { 154 struct mm_struct *mm = vma->vm_mm; 155 unsigned long addr = start; 156 int nr_pages = (end - start) / PAGE_SIZE; 157 int gup_flags; 158 159 VM_BUG_ON(start & ~PAGE_MASK); 160 VM_BUG_ON(end & ~PAGE_MASK); 161 VM_BUG_ON(start < vma->vm_start); 162 VM_BUG_ON(end > vma->vm_end); 163 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 164 165 gup_flags = FOLL_TOUCH | FOLL_MLOCK; 166 /* 167 * We want to touch writable mappings with a write fault in order 168 * to break COW, except for shared mappings because these don't COW 169 * and we would not want to dirty them for nothing. 170 */ 171 if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE) 172 gup_flags |= FOLL_WRITE; 173 174 /* 175 * We want mlock to succeed for regions that have any permissions 176 * other than PROT_NONE. 177 */ 178 if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) 179 gup_flags |= FOLL_FORCE; 180 181 return __get_user_pages(current, mm, addr, nr_pages, gup_flags, 182 NULL, NULL, nonblocking); 183 } 184 185 /* 186 * convert get_user_pages() return value to posix mlock() error 187 */ 188 static int __mlock_posix_error_return(long retval) 189 { 190 if (retval == -EFAULT) 191 retval = -ENOMEM; 192 else if (retval == -ENOMEM) 193 retval = -EAGAIN; 194 return retval; 195 } 196 197 /** 198 * mlock_vma_pages_range() - mlock pages in specified vma range. 199 * @vma - the vma containing the specfied address range 200 * @start - starting address in @vma to mlock 201 * @end - end address [+1] in @vma to mlock 202 * 203 * For mmap()/mremap()/expansion of mlocked vma. 204 * 205 * return 0 on success for "normal" vmas. 206 * 207 * return number of pages [> 0] to be removed from locked_vm on success 208 * of "special" vmas. 209 */ 210 long mlock_vma_pages_range(struct vm_area_struct *vma, 211 unsigned long start, unsigned long end) 212 { 213 int nr_pages = (end - start) / PAGE_SIZE; 214 BUG_ON(!(vma->vm_flags & VM_LOCKED)); 215 216 /* 217 * filter unlockable vmas 218 */ 219 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 220 goto no_mlock; 221 222 if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || 223 is_vm_hugetlb_page(vma) || 224 vma == get_gate_vma(current->mm))) { 225 226 __mlock_vma_pages_range(vma, start, end, NULL); 227 228 /* Hide errors from mmap() and other callers */ 229 return 0; 230 } 231 232 /* 233 * User mapped kernel pages or huge pages: 234 * make these pages present to populate the ptes, but 235 * fall thru' to reset VM_LOCKED--no need to unlock, and 236 * return nr_pages so these don't get counted against task's 237 * locked limit. huge pages are already counted against 238 * locked vm limit. 239 */ 240 make_pages_present(start, end); 241 242 no_mlock: 243 vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */ 244 return nr_pages; /* error or pages NOT mlocked */ 245 } 246 247 /* 248 * munlock_vma_pages_range() - munlock all pages in the vma range.' 249 * @vma - vma containing range to be munlock()ed. 250 * @start - start address in @vma of the range 251 * @end - end of range in @vma. 252 * 253 * For mremap(), munmap() and exit(). 254 * 255 * Called with @vma VM_LOCKED. 256 * 257 * Returns with VM_LOCKED cleared. Callers must be prepared to 258 * deal with this. 259 * 260 * We don't save and restore VM_LOCKED here because pages are 261 * still on lru. In unmap path, pages might be scanned by reclaim 262 * and re-mlocked by try_to_{munlock|unmap} before we unmap and 263 * free them. This will result in freeing mlocked pages. 264 */ 265 void munlock_vma_pages_range(struct vm_area_struct *vma, 266 unsigned long start, unsigned long end) 267 { 268 unsigned long addr; 269 270 lru_add_drain(); 271 vma->vm_flags &= ~VM_LOCKED; 272 273 for (addr = start; addr < end; addr += PAGE_SIZE) { 274 struct page *page; 275 /* 276 * Although FOLL_DUMP is intended for get_dump_page(), 277 * it just so happens that its special treatment of the 278 * ZERO_PAGE (returning an error instead of doing get_page) 279 * suits munlock very well (and if somehow an abnormal page 280 * has sneaked into the range, we won't oops here: great). 281 */ 282 page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); 283 if (page && !IS_ERR(page)) { 284 lock_page(page); 285 /* 286 * Like in __mlock_vma_pages_range(), 287 * because we lock page here and migration is 288 * blocked by the elevated reference, we need 289 * only check for file-cache page truncation. 290 */ 291 if (page->mapping) 292 munlock_vma_page(page); 293 unlock_page(page); 294 put_page(page); 295 } 296 cond_resched(); 297 } 298 } 299 300 /* 301 * mlock_fixup - handle mlock[all]/munlock[all] requests. 302 * 303 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and 304 * munlock is a no-op. However, for some special vmas, we go ahead and 305 * populate the ptes via make_pages_present(). 306 * 307 * For vmas that pass the filters, merge/split as appropriate. 308 */ 309 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, 310 unsigned long start, unsigned long end, unsigned int newflags) 311 { 312 struct mm_struct *mm = vma->vm_mm; 313 pgoff_t pgoff; 314 int nr_pages; 315 int ret = 0; 316 int lock = newflags & VM_LOCKED; 317 318 if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) || 319 is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm)) 320 goto out; /* don't set VM_LOCKED, don't count */ 321 322 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); 323 *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma, 324 vma->vm_file, pgoff, vma_policy(vma)); 325 if (*prev) { 326 vma = *prev; 327 goto success; 328 } 329 330 if (start != vma->vm_start) { 331 ret = split_vma(mm, vma, start, 1); 332 if (ret) 333 goto out; 334 } 335 336 if (end != vma->vm_end) { 337 ret = split_vma(mm, vma, end, 0); 338 if (ret) 339 goto out; 340 } 341 342 success: 343 /* 344 * Keep track of amount of locked VM. 345 */ 346 nr_pages = (end - start) >> PAGE_SHIFT; 347 if (!lock) 348 nr_pages = -nr_pages; 349 mm->locked_vm += nr_pages; 350 351 /* 352 * vm_flags is protected by the mmap_sem held in write mode. 353 * It's okay if try_to_unmap_one unmaps a page just after we 354 * set VM_LOCKED, __mlock_vma_pages_range will bring it back. 355 */ 356 357 if (lock) 358 vma->vm_flags = newflags; 359 else 360 munlock_vma_pages_range(vma, start, end); 361 362 out: 363 *prev = vma; 364 return ret; 365 } 366 367 static int do_mlock(unsigned long start, size_t len, int on) 368 { 369 unsigned long nstart, end, tmp; 370 struct vm_area_struct * vma, * prev; 371 int error; 372 373 VM_BUG_ON(start & ~PAGE_MASK); 374 VM_BUG_ON(len != PAGE_ALIGN(len)); 375 end = start + len; 376 if (end < start) 377 return -EINVAL; 378 if (end == start) 379 return 0; 380 vma = find_vma_prev(current->mm, start, &prev); 381 if (!vma || vma->vm_start > start) 382 return -ENOMEM; 383 384 if (start > vma->vm_start) 385 prev = vma; 386 387 for (nstart = start ; ; ) { 388 unsigned int newflags; 389 390 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ 391 392 newflags = vma->vm_flags | VM_LOCKED; 393 if (!on) 394 newflags &= ~VM_LOCKED; 395 396 tmp = vma->vm_end; 397 if (tmp > end) 398 tmp = end; 399 error = mlock_fixup(vma, &prev, nstart, tmp, newflags); 400 if (error) 401 break; 402 nstart = tmp; 403 if (nstart < prev->vm_end) 404 nstart = prev->vm_end; 405 if (nstart >= end) 406 break; 407 408 vma = prev->vm_next; 409 if (!vma || vma->vm_start != nstart) { 410 error = -ENOMEM; 411 break; 412 } 413 } 414 return error; 415 } 416 417 static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors) 418 { 419 struct mm_struct *mm = current->mm; 420 unsigned long end, nstart, nend; 421 struct vm_area_struct *vma = NULL; 422 int locked = 0; 423 int ret = 0; 424 425 VM_BUG_ON(start & ~PAGE_MASK); 426 VM_BUG_ON(len != PAGE_ALIGN(len)); 427 end = start + len; 428 429 for (nstart = start; nstart < end; nstart = nend) { 430 /* 431 * We want to fault in pages for [nstart; end) address range. 432 * Find first corresponding VMA. 433 */ 434 if (!locked) { 435 locked = 1; 436 down_read(&mm->mmap_sem); 437 vma = find_vma(mm, nstart); 438 } else if (nstart >= vma->vm_end) 439 vma = vma->vm_next; 440 if (!vma || vma->vm_start >= end) 441 break; 442 /* 443 * Set [nstart; nend) to intersection of desired address 444 * range with the first VMA. Also, skip undesirable VMA types. 445 */ 446 nend = min(end, vma->vm_end); 447 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 448 continue; 449 if (nstart < vma->vm_start) 450 nstart = vma->vm_start; 451 /* 452 * Now fault in a range of pages. __mlock_vma_pages_range() 453 * double checks the vma flags, so that it won't mlock pages 454 * if the vma was already munlocked. 455 */ 456 ret = __mlock_vma_pages_range(vma, nstart, nend, &locked); 457 if (ret < 0) { 458 if (ignore_errors) { 459 ret = 0; 460 continue; /* continue at next VMA */ 461 } 462 ret = __mlock_posix_error_return(ret); 463 break; 464 } 465 nend = nstart + ret * PAGE_SIZE; 466 ret = 0; 467 } 468 if (locked) 469 up_read(&mm->mmap_sem); 470 return ret; /* 0 or negative error code */ 471 } 472 473 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) 474 { 475 unsigned long locked; 476 unsigned long lock_limit; 477 int error = -ENOMEM; 478 479 if (!can_do_mlock()) 480 return -EPERM; 481 482 lru_add_drain_all(); /* flush pagevec */ 483 484 down_write(¤t->mm->mmap_sem); 485 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 486 start &= PAGE_MASK; 487 488 locked = len >> PAGE_SHIFT; 489 locked += current->mm->locked_vm; 490 491 lock_limit = rlimit(RLIMIT_MEMLOCK); 492 lock_limit >>= PAGE_SHIFT; 493 494 /* check against resource limits */ 495 if ((locked <= lock_limit) || capable(CAP_IPC_LOCK)) 496 error = do_mlock(start, len, 1); 497 up_write(¤t->mm->mmap_sem); 498 if (!error) 499 error = do_mlock_pages(start, len, 0); 500 return error; 501 } 502 503 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) 504 { 505 int ret; 506 507 down_write(¤t->mm->mmap_sem); 508 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 509 start &= PAGE_MASK; 510 ret = do_mlock(start, len, 0); 511 up_write(¤t->mm->mmap_sem); 512 return ret; 513 } 514 515 static int do_mlockall(int flags) 516 { 517 struct vm_area_struct * vma, * prev = NULL; 518 unsigned int def_flags = 0; 519 520 if (flags & MCL_FUTURE) 521 def_flags = VM_LOCKED; 522 current->mm->def_flags = def_flags; 523 if (flags == MCL_FUTURE) 524 goto out; 525 526 for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { 527 unsigned int newflags; 528 529 newflags = vma->vm_flags | VM_LOCKED; 530 if (!(flags & MCL_CURRENT)) 531 newflags &= ~VM_LOCKED; 532 533 /* Ignore errors */ 534 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); 535 } 536 out: 537 return 0; 538 } 539 540 SYSCALL_DEFINE1(mlockall, int, flags) 541 { 542 unsigned long lock_limit; 543 int ret = -EINVAL; 544 545 if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE))) 546 goto out; 547 548 ret = -EPERM; 549 if (!can_do_mlock()) 550 goto out; 551 552 lru_add_drain_all(); /* flush pagevec */ 553 554 down_write(¤t->mm->mmap_sem); 555 556 lock_limit = rlimit(RLIMIT_MEMLOCK); 557 lock_limit >>= PAGE_SHIFT; 558 559 ret = -ENOMEM; 560 if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) || 561 capable(CAP_IPC_LOCK)) 562 ret = do_mlockall(flags); 563 up_write(¤t->mm->mmap_sem); 564 if (!ret && (flags & MCL_CURRENT)) { 565 /* Ignore errors */ 566 do_mlock_pages(0, TASK_SIZE, 1); 567 } 568 out: 569 return ret; 570 } 571 572 SYSCALL_DEFINE0(munlockall) 573 { 574 int ret; 575 576 down_write(¤t->mm->mmap_sem); 577 ret = do_mlockall(0); 578 up_write(¤t->mm->mmap_sem); 579 return ret; 580 } 581 582 /* 583 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB 584 * shm segments) get accounted against the user_struct instead. 585 */ 586 static DEFINE_SPINLOCK(shmlock_user_lock); 587 588 int user_shm_lock(size_t size, struct user_struct *user) 589 { 590 unsigned long lock_limit, locked; 591 int allowed = 0; 592 593 locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 594 lock_limit = rlimit(RLIMIT_MEMLOCK); 595 if (lock_limit == RLIM_INFINITY) 596 allowed = 1; 597 lock_limit >>= PAGE_SHIFT; 598 spin_lock(&shmlock_user_lock); 599 if (!allowed && 600 locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK)) 601 goto out; 602 get_uid(user); 603 user->locked_shm += locked; 604 allowed = 1; 605 out: 606 spin_unlock(&shmlock_user_lock); 607 return allowed; 608 } 609 610 void user_shm_unlock(size_t size, struct user_struct *user) 611 { 612 spin_lock(&shmlock_user_lock); 613 user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 614 spin_unlock(&shmlock_user_lock); 615 free_uid(user); 616 } 617