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/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         /* Serialize with page migration */
  80         BUG_ON(!PageLocked(page));
  81
  82         if (!TestSetPageMlocked(page)) {
  83                 mod_zone_page_state(page_zone(page), NR_MLOCK,
  84                                     hpage_nr_pages(page));
  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 unsigned int munlock_vma_page(struct page *page)
 107 {
 108         unsigned int page_mask = 0;
 109
 110         /* For try_to_munlock() and to serialize with page migration */
 111         BUG_ON(!PageLocked(page));
 112
 113         if (TestClearPageMlocked(page)) {
 114                 unsigned int nr_pages = hpage_nr_pages(page);
 115                 mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
 116                 page_mask = nr_pages - 1;
 117                 if (!isolate_lru_page(page)) {
 118                         int ret = SWAP_AGAIN;
 119
 120                         /*
 121                          * Optimization: if the page was mapped just once,
 122                          * that's our mapping and we don't need to check all the
 123                          * other vmas.
 124                          */
 125                         if (page_mapcount(page) > 1)
 126                                 ret = try_to_munlock(page);
 127                         /*
 128                          * did try_to_unlock() succeed or punt?
 129                          */
 130                         if (ret != SWAP_MLOCK)
 131                                 count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 132
 133                         putback_lru_page(page);
 134                 } else {
 135                         /*
 136                          * Some other task has removed the page from the LRU.
 137                          * putback_lru_page() will take care of removing the
 138                          * page from the unevictable list, if necessary.
 139                          * vmscan [page_referenced()] will move the page back
 140                          * to the unevictable list if some other vma has it
 141                          * mlocked.
 142                          */
 143                         if (PageUnevictable(page))
 144                                 count_vm_event(UNEVICTABLE_PGSTRANDED);
 145                         else
 146                                 count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 147                 }
 148         }
 149
 150         return page_mask;
 151 }
 152
 153 /**
 154  * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
 155  * @vma:   target vma
 156  * @start: start address
 157  * @end:   end address
 158  *
 159  * This takes care of making the pages present too.
 160  *
 161  * return 0 on success, negative error code on error.
 162  *
 163  * vma->vm_mm->mmap_sem must be held for at least read.
 164  */
 165 long __mlock_vma_pages_range(struct vm_area_struct *vma,
 166                 unsigned long start, unsigned long end, int *nonblocking)
 167 {
 168         struct mm_struct *mm = vma->vm_mm;
 169         unsigned long nr_pages = (end - start) / PAGE_SIZE;
 170         int gup_flags;
 171
 172         VM_BUG_ON(start & ~PAGE_MASK);
 173         VM_BUG_ON(end   & ~PAGE_MASK);
 174         VM_BUG_ON(start < vma->vm_start);
 175         VM_BUG_ON(end   > vma->vm_end);
 176         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 177
 178         gup_flags = FOLL_TOUCH | FOLL_MLOCK;
 179         /*
 180          * We want to touch writable mappings with a write fault in order
 181          * to break COW, except for shared mappings because these don't COW
 182          * and we would not want to dirty them for nothing.
 183          */
 184         if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
 185                 gup_flags |= FOLL_WRITE;
 186
 187         /*
 188          * We want mlock to succeed for regions that have any permissions
 189          * other than PROT_NONE.
 190          */
 191         if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
 192                 gup_flags |= FOLL_FORCE;
 193
 194         /*
 195          * We made sure addr is within a VMA, so the following will
 196          * not result in a stack expansion that recurses back here.
 197          */
 198         return __get_user_pages(current, mm, start, nr_pages, gup_flags,
 199                                 NULL, NULL, nonblocking);
 200 }
 201
 202 /*
 203  * convert get_user_pages() return value to posix mlock() error
 204  */
 205 static int __mlock_posix_error_return(long retval)
 206 {
 207         if (retval == -EFAULT)
 208                 retval = -ENOMEM;
 209         else if (retval == -ENOMEM)
 210                 retval = -EAGAIN;
 211         return retval;
 212 }
 213
 214 /*
 215  * munlock_vma_pages_range() - munlock all pages in the vma range.'
 216  * @vma - vma containing range to be munlock()ed.
 217  * @start - start address in @vma of the range
 218  * @end - end of range in @vma.
 219  *
 220  *  For mremap(), munmap() and exit().
 221  *
 222  * Called with @vma VM_LOCKED.
 223  *
 224  * Returns with VM_LOCKED cleared.  Callers must be prepared to
 225  * deal with this.
 226  *
 227  * We don't save and restore VM_LOCKED here because pages are
 228  * still on lru.  In unmap path, pages might be scanned by reclaim
 229  * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 230  * free them.  This will result in freeing mlocked pages.
 231  */
 232 void munlock_vma_pages_range(struct vm_area_struct *vma,
 233                              unsigned long start, unsigned long end)
 234 {
 235         vma->vm_flags &= ~VM_LOCKED;
 236
 237         while (start < end) {
 238                 struct page *page;
 239                 unsigned int page_mask, page_increm;
 240
 241                 /*
 242                  * Although FOLL_DUMP is intended for get_dump_page(),
 243                  * it just so happens that its special treatment of the
 244                  * ZERO_PAGE (returning an error instead of doing get_page)
 245                  * suits munlock very well (and if somehow an abnormal page
 246                  * has sneaked into the range, we won't oops here: great).
 247                  */
 248                 page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
 249                                         &page_mask);
 250                 if (page && !IS_ERR(page)) {
 251                         lock_page(page);
 252                         lru_add_drain();
 253                         /*
 254                          * Any THP page found by follow_page_mask() may have
 255                          * gotten split before reaching munlock_vma_page(),
 256                          * so we need to recompute the page_mask here.
 257                          */
 258                         page_mask = munlock_vma_page(page);
 259                         unlock_page(page);
 260                         put_page(page);
 261                 }
 262                 page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
 263                 start += page_increm * PAGE_SIZE;
 264                 cond_resched();
 265         }
 266 }
 267
 268 /*
 269  * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 270  *
 271  * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 272  * munlock is a no-op.  However, for some special vmas, we go ahead and
 273  * populate the ptes.
 274  *
 275  * For vmas that pass the filters, merge/split as appropriate.
 276  */
 277 static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 278         unsigned long start, unsigned long end, vm_flags_t newflags)
 279 {
 280         struct mm_struct *mm = vma->vm_mm;
 281         pgoff_t pgoff;
 282         int nr_pages;
 283         int ret = 0;
 284         int lock = !!(newflags & VM_LOCKED);
 285
 286         if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
 287             is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
 288                 goto out;       /* don't set VM_LOCKED,  don't count */
 289
 290         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 291         *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 292                           vma->vm_file, pgoff, vma_policy(vma),
 293                           vma_get_anon_name(vma));
 294         if (*prev) {
 295                 vma = *prev;
 296                 goto success;
 297         }
 298
 299         if (start != vma->vm_start) {
 300                 ret = split_vma(mm, vma, start, 1);
 301                 if (ret)
 302                         goto out;
 303         }
 304
 305         if (end != vma->vm_end) {
 306                 ret = split_vma(mm, vma, end, 0);
 307                 if (ret)
 308                         goto out;
 309         }
 310
 311 success:
 312         /*
 313          * Keep track of amount of locked VM.
 314          */
 315         nr_pages = (end - start) >> PAGE_SHIFT;
 316         if (!lock)
 317                 nr_pages = -nr_pages;
 318         mm->locked_vm += nr_pages;
 319
 320         /*
 321          * vm_flags is protected by the mmap_sem held in write mode.
 322          * It's okay if try_to_unmap_one unmaps a page just after we
 323          * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 324          */
 325
 326         if (lock)
 327                 vma->vm_flags = newflags;
 328         else
 329                 munlock_vma_pages_range(vma, start, end);
 330
 331 out:
 332         *prev = vma;
 333         return ret;
 334 }
 335
 336 static int do_mlock(unsigned long start, size_t len, int on)
 337 {
 338         unsigned long nstart, end, tmp;
 339         struct vm_area_struct * vma, * prev;
 340         int error;
 341
 342         VM_BUG_ON(start & ~PAGE_MASK);
 343         VM_BUG_ON(len != PAGE_ALIGN(len));
 344         end = start + len;
 345         if (end < start)
 346                 return -EINVAL;
 347         if (end == start)
 348                 return 0;
 349         vma = find_vma(current->mm, start);
 350         if (!vma || vma->vm_start > start)
 351                 return -ENOMEM;
 352
 353         prev = vma->vm_prev;
 354         if (start > vma->vm_start)
 355                 prev = vma;
 356
 357         for (nstart = start ; ; ) {
 358                 vm_flags_t newflags;
 359
 360                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 361
 362                 newflags = vma->vm_flags & ~VM_LOCKED;
 363                 if (on)
 364                         newflags |= VM_LOCKED;
 365
 366                 tmp = vma->vm_end;
 367                 if (tmp > end)
 368                         tmp = end;
 369                 error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 370                 if (error)
 371                         break;
 372                 nstart = tmp;
 373                 if (nstart < prev->vm_end)
 374                         nstart = prev->vm_end;
 375                 if (nstart >= end)
 376                         break;
 377
 378                 vma = prev->vm_next;
 379                 if (!vma || vma->vm_start != nstart) {
 380                         error = -ENOMEM;
 381                         break;
 382                 }
 383         }
 384         return error;
 385 }
 386
 387 /*
 388  * __mm_populate - populate and/or mlock pages within a range of address space.
 389  *
 390  * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
 391  * flags. VMAs must be already marked with the desired vm_flags, and
 392  * mmap_sem must not be held.
 393  */
 394 int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
 395 {
 396         struct mm_struct *mm = current->mm;
 397         unsigned long end, nstart, nend;
 398         struct vm_area_struct *vma = NULL;
 399         int locked = 0;
 400         long ret = 0;
 401
 402         VM_BUG_ON(start & ~PAGE_MASK);
 403         VM_BUG_ON(len != PAGE_ALIGN(len));
 404         end = start + len;
 405
 406         for (nstart = start; nstart < end; nstart = nend) {
 407                 /*
 408                  * We want to fault in pages for [nstart; end) address range.
 409                  * Find first corresponding VMA.
 410                  */
 411                 if (!locked) {
 412                         locked = 1;
 413                         down_read(&mm->mmap_sem);
 414                         vma = find_vma(mm, nstart);
 415                 } else if (nstart >= vma->vm_end)
 416                         vma = vma->vm_next;
 417                 if (!vma || vma->vm_start >= end)
 418                         break;
 419                 /*
 420                  * Set [nstart; nend) to intersection of desired address
 421                  * range with the first VMA. Also, skip undesirable VMA types.
 422                  */
 423                 nend = min(end, vma->vm_end);
 424                 if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 425                         continue;
 426                 if (nstart < vma->vm_start)
 427                         nstart = vma->vm_start;
 428                 /*
 429                  * Now fault in a range of pages. __mlock_vma_pages_range()
 430                  * double checks the vma flags, so that it won't mlock pages
 431                  * if the vma was already munlocked.
 432                  */
 433                 ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
 434                 if (ret < 0) {
 435                         if (ignore_errors) {
 436                                 ret = 0;
 437                                 continue;       /* continue at next VMA */
 438                         }
 439                         ret = __mlock_posix_error_return(ret);
 440                         break;
 441                 }
 442                 nend = nstart + ret * PAGE_SIZE;
 443                 ret = 0;
 444         }
 445         if (locked)
 446                 up_read(&mm->mmap_sem);
 447         return ret;     /* 0 or negative error code */
 448 }
 449
 450 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 451 {
 452         unsigned long locked;
 453         unsigned long lock_limit;
 454         int error = -ENOMEM;
 455
 456         if (!can_do_mlock())
 457                 return -EPERM;
 458
 459         lru_add_drain_all();    /* flush pagevec */
 460
 461         down_write(&current->mm->mmap_sem);
 462         len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 463         start &= PAGE_MASK;
 464
 465         locked = len >> PAGE_SHIFT;
 466         locked += current->mm->locked_vm;
 467
 468         lock_limit = rlimit(RLIMIT_MEMLOCK);
 469         lock_limit >>= PAGE_SHIFT;
 470
 471         /* check against resource limits */
 472         if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 473                 error = do_mlock(start, len, 1);
 474         up_write(&current->mm->mmap_sem);
 475         if (!error)
 476                 error = __mm_populate(start, len, 0);
 477         return error;
 478 }
 479
 480 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 481 {
 482         int ret;
 483
 484         down_write(&current->mm->mmap_sem);
 485         len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 486         start &= PAGE_MASK;
 487         ret = do_mlock(start, len, 0);
 488         up_write(&current->mm->mmap_sem);
 489         return ret;
 490 }
 491
 492 static int do_mlockall(int flags)
 493 {
 494         struct vm_area_struct * vma, * prev = NULL;
 495
 496         if (flags & MCL_FUTURE)
 497                 current->mm->def_flags |= VM_LOCKED;
 498         else
 499                 current->mm->def_flags &= ~VM_LOCKED;
 500         if (flags == MCL_FUTURE)
 501                 goto out;
 502
 503         for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 504                 vm_flags_t newflags;
 505
 506                 newflags = vma->vm_flags & ~VM_LOCKED;
 507                 if (flags & MCL_CURRENT)
 508                         newflags |= VM_LOCKED;
 509
 510                 /* Ignore errors */
 511                 mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 512         }
 513 out:
 514         return 0;
 515 }
 516
 517 SYSCALL_DEFINE1(mlockall, int, flags)
 518 {
 519         unsigned long lock_limit;
 520         int ret = -EINVAL;
 521
 522         if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 523                 goto out;
 524
 525         ret = -EPERM;
 526         if (!can_do_mlock())
 527                 goto out;
 528
 529         if (flags & MCL_CURRENT)
 530                 lru_add_drain_all();    /* flush pagevec */
 531
 532         down_write(&current->mm->mmap_sem);
 533
 534         lock_limit = rlimit(RLIMIT_MEMLOCK);
 535         lock_limit >>= PAGE_SHIFT;
 536
 537         ret = -ENOMEM;
 538         if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 539             capable(CAP_IPC_LOCK))
 540                 ret = do_mlockall(flags);
 541         up_write(&current->mm->mmap_sem);
 542         if (!ret && (flags & MCL_CURRENT))
 543                 mm_populate(0, TASK_SIZE);
 544 out:
 545         return ret;
 546 }
 547
 548 SYSCALL_DEFINE0(munlockall)
 549 {
 550         int ret;
 551
 552         down_write(&current->mm->mmap_sem);
 553         ret = do_mlockall(0);
 554         up_write(&current->mm->mmap_sem);
 555         return ret;
 556 }
 557
 558 /*
 559  * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 560  * shm segments) get accounted against the user_struct instead.
 561  */
 562 static DEFINE_SPINLOCK(shmlock_user_lock);
 563
 564 int user_shm_lock(size_t size, struct user_struct *user)
 565 {
 566         unsigned long lock_limit, locked;
 567         int allowed = 0;
 568
 569         locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 570         lock_limit = rlimit(RLIMIT_MEMLOCK);
 571         if (lock_limit == RLIM_INFINITY)
 572                 allowed = 1;
 573         lock_limit >>= PAGE_SHIFT;
 574         spin_lock(&shmlock_user_lock);
 575         if (!allowed &&
 576             locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 577                 goto out;
 578         get_uid(user);
 579         user->locked_shm += locked;
 580         allowed = 1;
 581 out:
 582         spin_unlock(&shmlock_user_lock);
 583         return allowed;
 584 }
 585
 586 void user_shm_unlock(size_t size, struct user_struct *user)
 587 {
 588         spin_lock(&shmlock_user_lock);
 589         user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 590         spin_unlock(&shmlock_user_lock);
 591         free_uid(user);
 592 }