mm/mlock.c

   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(&current->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(&current->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(&current->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(&current->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(&current->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(&current->mm->mmap_sem);
 561 out:
 562         return ret;
 563 }
 564
 565 SYSCALL_DEFINE0(munlockall)
 566 {
 567         int ret;
 568
 569         down_write(&current->mm->mmap_sem);
 570         ret = do_mlockall(0);
 571         up_write(&current->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 }