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 { 153 struct mm_struct *mm = vma->vm_mm; 154 unsigned long addr = start; 155 struct page *pages[16]; /* 16 gives a reasonable batch */ 156 int nr_pages = (end - start) / PAGE_SIZE; 157 int ret = 0; 158 int gup_flags; 159 160 VM_BUG_ON(start & ~PAGE_MASK); 161 VM_BUG_ON(end & ~PAGE_MASK); 162 VM_BUG_ON(start < vma->vm_start); 163 VM_BUG_ON(end > vma->vm_end); 164 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 165 166 gup_flags = FOLL_TOUCH | FOLL_GET; 167 if (vma->vm_flags & VM_WRITE) 168 gup_flags |= FOLL_WRITE; 169 170 /* We don't try to access the guard page of a stack vma */ 171 if (vma->vm_flags & VM_GROWSDOWN) { 172 if (start == vma->vm_start) { 173 start += PAGE_SIZE; 174 nr_pages--; 175 } 176 } 177 178 while (nr_pages > 0) { 179 int i; 180 181 cond_resched(); 182 183 /* 184 * get_user_pages makes pages present if we are 185 * setting mlock. and this extra reference count will 186 * disable migration of this page. However, page may 187 * still be truncated out from under us. 188 */ 189 ret = __get_user_pages(current, mm, addr, 190 min_t(int, nr_pages, ARRAY_SIZE(pages)), 191 gup_flags, pages, NULL); 192 /* 193 * This can happen for, e.g., VM_NONLINEAR regions before 194 * a page has been allocated and mapped at a given offset, 195 * or for addresses that map beyond end of a file. 196 * We'll mlock the pages if/when they get faulted in. 197 */ 198 if (ret < 0) 199 break; 200 201 lru_add_drain(); /* push cached pages to LRU */ 202 203 for (i = 0; i < ret; i++) { 204 struct page *page = pages[i]; 205 206 if (page->mapping) { 207 /* 208 * That preliminary check is mainly to avoid 209 * the pointless overhead of lock_page on the 210 * ZERO_PAGE: which might bounce very badly if 211 * there is contention. However, we're still 212 * dirtying its cacheline with get/put_page: 213 * we'll add another __get_user_pages flag to 214 * avoid it if that case turns out to matter. 215 */ 216 lock_page(page); 217 /* 218 * Because we lock page here and migration is 219 * blocked by the elevated reference, we need 220 * only check for file-cache page truncation. 221 */ 222 if (page->mapping) 223 mlock_vma_page(page); 224 unlock_page(page); 225 } 226 put_page(page); /* ref from get_user_pages() */ 227 } 228 229 addr += ret * PAGE_SIZE; 230 nr_pages -= ret; 231 ret = 0; 232 } 233 234 return ret; /* 0 or negative error code */ 235 } 236 237 /* 238 * convert get_user_pages() return value to posix mlock() error 239 */ 240 static int __mlock_posix_error_return(long retval) 241 { 242 if (retval == -EFAULT) 243 retval = -ENOMEM; 244 else if (retval == -ENOMEM) 245 retval = -EAGAIN; 246 return retval; 247 } 248 249 /** 250 * mlock_vma_pages_range() - mlock pages in specified vma range. 251 * @vma - the vma containing the specfied address range 252 * @start - starting address in @vma to mlock 253 * @end - end address [+1] in @vma to mlock 254 * 255 * For mmap()/mremap()/expansion of mlocked vma. 256 * 257 * return 0 on success for "normal" vmas. 258 * 259 * return number of pages [> 0] to be removed from locked_vm on success 260 * of "special" vmas. 261 */ 262 long mlock_vma_pages_range(struct vm_area_struct *vma, 263 unsigned long start, unsigned long end) 264 { 265 int nr_pages = (end - start) / PAGE_SIZE; 266 BUG_ON(!(vma->vm_flags & VM_LOCKED)); 267 268 /* 269 * filter unlockable vmas 270 */ 271 if (vma->vm_flags & (VM_IO | VM_PFNMAP)) 272 goto no_mlock; 273 274 if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || 275 is_vm_hugetlb_page(vma) || 276 vma == get_gate_vma(current))) { 277 278 __mlock_vma_pages_range(vma, start, end); 279 280 /* Hide errors from mmap() and other callers */ 281 return 0; 282 } 283 284 /* 285 * User mapped kernel pages or huge pages: 286 * make these pages present to populate the ptes, but 287 * fall thru' to reset VM_LOCKED--no need to unlock, and 288 * return nr_pages so these don't get counted against task's 289 * locked limit. huge pages are already counted against 290 * locked vm limit. 291 */ 292 make_pages_present(start, end); 293 294 no_mlock: 295 vma->vm_flags &= ~VM_LOCKED; /* and don't come back! */ 296 return nr_pages; /* error or pages NOT mlocked */ 297 } 298 299 /* 300 * munlock_vma_pages_range() - munlock all pages in the vma range.' 301 * @vma - vma containing range to be munlock()ed. 302 * @start - start address in @vma of the range 303 * @end - end of range in @vma. 304 * 305 * For mremap(), munmap() and exit(). 306 * 307 * Called with @vma VM_LOCKED. 308 * 309 * Returns with VM_LOCKED cleared. Callers must be prepared to 310 * deal with this. 311 * 312 * We don't save and restore VM_LOCKED here because pages are 313 * still on lru. In unmap path, pages might be scanned by reclaim 314 * and re-mlocked by try_to_{munlock|unmap} before we unmap and 315 * free them. This will result in freeing mlocked pages. 316 */ 317 void munlock_vma_pages_range(struct vm_area_struct *vma, 318 unsigned long start, unsigned long end) 319 { 320 unsigned long addr; 321 322 lru_add_drain(); 323 vma->vm_flags &= ~VM_LOCKED; 324 325 for (addr = start; addr < end; addr += PAGE_SIZE) { 326 struct page *page; 327 /* 328 * Although FOLL_DUMP is intended for get_dump_page(), 329 * it just so happens that its special treatment of the 330 * ZERO_PAGE (returning an error instead of doing get_page) 331 * suits munlock very well (and if somehow an abnormal page 332 * has sneaked into the range, we won't oops here: great). 333 */ 334 page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP); 335 if (page && !IS_ERR(page)) { 336 lock_page(page); 337 /* 338 * Like in __mlock_vma_pages_range(), 339 * because we lock page here and migration is 340 * blocked by the elevated reference, we need 341 * only check for file-cache page truncation. 342 */ 343 if (page->mapping) 344 munlock_vma_page(page); 345 unlock_page(page); 346 put_page(page); 347 } 348 cond_resched(); 349 } 350 } 351 352 /* 353 * mlock_fixup - handle mlock[all]/munlock[all] requests. 354 * 355 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and 356 * munlock is a no-op. However, for some special vmas, we go ahead and 357 * populate the ptes via make_pages_present(). 358 * 359 * For vmas that pass the filters, merge/split as appropriate. 360 */ 361 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, 362 unsigned long start, unsigned long end, unsigned int newflags) 363 { 364 struct mm_struct *mm = vma->vm_mm; 365 pgoff_t pgoff; 366 int nr_pages; 367 int ret = 0; 368 int lock = newflags & VM_LOCKED; 369 370 if (newflags == vma->vm_flags || 371 (vma->vm_flags & (VM_IO | VM_PFNMAP))) 372 goto out; /* don't set VM_LOCKED, don't count */ 373 374 if ((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) || 375 is_vm_hugetlb_page(vma) || 376 vma == get_gate_vma(current)) { 377 if (lock) 378 make_pages_present(start, end); 379 goto out; /* don't set VM_LOCKED, don't count */ 380 } 381 382 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT); 383 *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma, 384 vma->vm_file, pgoff, vma_policy(vma)); 385 if (*prev) { 386 vma = *prev; 387 goto success; 388 } 389 390 if (start != vma->vm_start) { 391 ret = split_vma(mm, vma, start, 1); 392 if (ret) 393 goto out; 394 } 395 396 if (end != vma->vm_end) { 397 ret = split_vma(mm, vma, end, 0); 398 if (ret) 399 goto out; 400 } 401 402 success: 403 /* 404 * Keep track of amount of locked VM. 405 */ 406 nr_pages = (end - start) >> PAGE_SHIFT; 407 if (!lock) 408 nr_pages = -nr_pages; 409 mm->locked_vm += nr_pages; 410 411 /* 412 * vm_flags is protected by the mmap_sem held in write mode. 413 * It's okay if try_to_unmap_one unmaps a page just after we 414 * set VM_LOCKED, __mlock_vma_pages_range will bring it back. 415 */ 416 417 if (lock) { 418 vma->vm_flags = newflags; 419 ret = __mlock_vma_pages_range(vma, start, end); 420 if (ret < 0) 421 ret = __mlock_posix_error_return(ret); 422 } else { 423 munlock_vma_pages_range(vma, start, end); 424 } 425 426 out: 427 *prev = vma; 428 return ret; 429 } 430 431 static int do_mlock(unsigned long start, size_t len, int on) 432 { 433 unsigned long nstart, end, tmp; 434 struct vm_area_struct * vma, * prev; 435 int error; 436 437 len = PAGE_ALIGN(len); 438 end = start + len; 439 if (end < start) 440 return -EINVAL; 441 if (end == start) 442 return 0; 443 vma = find_vma_prev(current->mm, start, &prev); 444 if (!vma || vma->vm_start > start) 445 return -ENOMEM; 446 447 if (start > vma->vm_start) 448 prev = vma; 449 450 for (nstart = start ; ; ) { 451 unsigned int newflags; 452 453 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */ 454 455 newflags = vma->vm_flags | VM_LOCKED; 456 if (!on) 457 newflags &= ~VM_LOCKED; 458 459 tmp = vma->vm_end; 460 if (tmp > end) 461 tmp = end; 462 error = mlock_fixup(vma, &prev, nstart, tmp, newflags); 463 if (error) 464 break; 465 nstart = tmp; 466 if (nstart < prev->vm_end) 467 nstart = prev->vm_end; 468 if (nstart >= end) 469 break; 470 471 vma = prev->vm_next; 472 if (!vma || vma->vm_start != nstart) { 473 error = -ENOMEM; 474 break; 475 } 476 } 477 return error; 478 } 479 480 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) 481 { 482 unsigned long locked; 483 unsigned long lock_limit; 484 int error = -ENOMEM; 485 486 if (!can_do_mlock()) 487 return -EPERM; 488 489 lru_add_drain_all(); /* flush pagevec */ 490 491 down_write(¤t->mm->mmap_sem); 492 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 493 start &= PAGE_MASK; 494 495 locked = len >> PAGE_SHIFT; 496 locked += current->mm->locked_vm; 497 498 lock_limit = rlimit(RLIMIT_MEMLOCK); 499 lock_limit >>= PAGE_SHIFT; 500 501 /* check against resource limits */ 502 if ((locked <= lock_limit) || capable(CAP_IPC_LOCK)) 503 error = do_mlock(start, len, 1); 504 up_write(¤t->mm->mmap_sem); 505 return error; 506 } 507 508 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) 509 { 510 int ret; 511 512 down_write(¤t->mm->mmap_sem); 513 len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); 514 start &= PAGE_MASK; 515 ret = do_mlock(start, len, 0); 516 up_write(¤t->mm->mmap_sem); 517 return ret; 518 } 519 520 static int do_mlockall(int flags) 521 { 522 struct vm_area_struct * vma, * prev = NULL; 523 unsigned int def_flags = 0; 524 525 if (flags & MCL_FUTURE) 526 def_flags = VM_LOCKED; 527 current->mm->def_flags = def_flags; 528 if (flags == MCL_FUTURE) 529 goto out; 530 531 for (vma = current->mm->mmap; vma ; vma = prev->vm_next) { 532 unsigned int newflags; 533 534 newflags = vma->vm_flags | VM_LOCKED; 535 if (!(flags & MCL_CURRENT)) 536 newflags &= ~VM_LOCKED; 537 538 /* Ignore errors */ 539 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags); 540 } 541 out: 542 return 0; 543 } 544 545 SYSCALL_DEFINE1(mlockall, int, flags) 546 { 547 unsigned long lock_limit; 548 int ret = -EINVAL; 549 550 if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE))) 551 goto out; 552 553 ret = -EPERM; 554 if (!can_do_mlock()) 555 goto out; 556 557 lru_add_drain_all(); /* flush pagevec */ 558 559 down_write(¤t->mm->mmap_sem); 560 561 lock_limit = rlimit(RLIMIT_MEMLOCK); 562 lock_limit >>= PAGE_SHIFT; 563 564 ret = -ENOMEM; 565 if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) || 566 capable(CAP_IPC_LOCK)) 567 ret = do_mlockall(flags); 568 up_write(¤t->mm->mmap_sem); 569 out: 570 return ret; 571 } 572 573 SYSCALL_DEFINE0(munlockall) 574 { 575 int ret; 576 577 down_write(¤t->mm->mmap_sem); 578 ret = do_mlockall(0); 579 up_write(¤t->mm->mmap_sem); 580 return ret; 581 } 582 583 /* 584 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB 585 * shm segments) get accounted against the user_struct instead. 586 */ 587 static DEFINE_SPINLOCK(shmlock_user_lock); 588 589 int user_shm_lock(size_t size, struct user_struct *user) 590 { 591 unsigned long lock_limit, locked; 592 int allowed = 0; 593 594 locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 595 lock_limit = rlimit(RLIMIT_MEMLOCK); 596 if (lock_limit == RLIM_INFINITY) 597 allowed = 1; 598 lock_limit >>= PAGE_SHIFT; 599 spin_lock(&shmlock_user_lock); 600 if (!allowed && 601 locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK)) 602 goto out; 603 get_uid(user); 604 user->locked_shm += locked; 605 allowed = 1; 606 out: 607 spin_unlock(&shmlock_user_lock); 608 return allowed; 609 } 610 611 void user_shm_unlock(size_t size, struct user_struct *user) 612 { 613 spin_lock(&shmlock_user_lock); 614 user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT; 615 spin_unlock(&shmlock_user_lock); 616 free_uid(user); 617 } 618