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