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