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