linux/mm/mlock.c
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   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
  24int 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}
  32EXPORT_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 */
  54void __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 */
  79void 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 */
 106void 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
 138static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
 139{
 140        return (vma->vm_flags & VM_GROWSDOWN) &&
 141                (vma->vm_start == addr) &&
 142                !vma_stack_continue(vma->vm_prev, addr);
 143}
 144
 145/**
 146 * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
 147 * @vma:   target vma
 148 * @start: start address
 149 * @end:   end address
 150 *
 151 * This takes care of making the pages present too.
 152 *
 153 * return 0 on success, negative error code on error.
 154 *
 155 * vma->vm_mm->mmap_sem must be held for at least read.
 156 */
 157static long __mlock_vma_pages_range(struct vm_area_struct *vma,
 158                                    unsigned long start, unsigned long end,
 159                                    int *nonblocking)
 160{
 161        struct mm_struct *mm = vma->vm_mm;
 162        unsigned long addr = start;
 163        int nr_pages = (end - start) / PAGE_SIZE;
 164        int gup_flags;
 165
 166        VM_BUG_ON(start & ~PAGE_MASK);
 167        VM_BUG_ON(end   & ~PAGE_MASK);
 168        VM_BUG_ON(start < vma->vm_start);
 169        VM_BUG_ON(end   > vma->vm_end);
 170        VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 171
 172        gup_flags = FOLL_TOUCH;
 173        /*
 174         * We want to touch writable mappings with a write fault in order
 175         * to break COW, except for shared mappings because these don't COW
 176         * and we would not want to dirty them for nothing.
 177         */
 178        if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
 179                gup_flags |= FOLL_WRITE;
 180
 181        /*
 182         * We want mlock to succeed for regions that have any permissions
 183         * other than PROT_NONE.
 184         */
 185        if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
 186                gup_flags |= FOLL_FORCE;
 187
 188        if (vma->vm_flags & VM_LOCKED)
 189                gup_flags |= FOLL_MLOCK;
 190
 191        /* We don't try to access the guard page of a stack vma */
 192        if (stack_guard_page(vma, start)) {
 193                addr += PAGE_SIZE;
 194                nr_pages--;
 195        }
 196
 197        return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
 198                                NULL, NULL, nonblocking);
 199}
 200
 201/*
 202 * convert get_user_pages() return value to posix mlock() error
 203 */
 204static int __mlock_posix_error_return(long retval)
 205{
 206        if (retval == -EFAULT)
 207                retval = -ENOMEM;
 208        else if (retval == -ENOMEM)
 209                retval = -EAGAIN;
 210        return retval;
 211}
 212
 213/**
 214 * mlock_vma_pages_range() - mlock pages in specified vma range.
 215 * @vma - the vma containing the specfied address range
 216 * @start - starting address in @vma to mlock
 217 * @end   - end address [+1] in @vma to mlock
 218 *
 219 * For mmap()/mremap()/expansion of mlocked vma.
 220 *
 221 * return 0 on success for "normal" vmas.
 222 *
 223 * return number of pages [> 0] to be removed from locked_vm on success
 224 * of "special" vmas.
 225 */
 226long mlock_vma_pages_range(struct vm_area_struct *vma,
 227                        unsigned long start, unsigned long end)
 228{
 229        int nr_pages = (end - start) / PAGE_SIZE;
 230        BUG_ON(!(vma->vm_flags & VM_LOCKED));
 231
 232        /*
 233         * filter unlockable vmas
 234         */
 235        if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 236                goto no_mlock;
 237
 238        if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 239                        is_vm_hugetlb_page(vma) ||
 240                        vma == get_gate_vma(current))) {
 241
 242                __mlock_vma_pages_range(vma, start, end, NULL);
 243
 244                /* Hide errors from mmap() and other callers */
 245                return 0;
 246        }
 247
 248        /*
 249         * User mapped kernel pages or huge pages:
 250         * make these pages present to populate the ptes, but
 251         * fall thru' to reset VM_LOCKED--no need to unlock, and
 252         * return nr_pages so these don't get counted against task's
 253         * locked limit.  huge pages are already counted against
 254         * locked vm limit.
 255         */
 256        make_pages_present(start, end);
 257
 258no_mlock:
 259        vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
 260        return nr_pages;                /* error or pages NOT mlocked */
 261}
 262
 263/*
 264 * munlock_vma_pages_range() - munlock all pages in the vma range.'
 265 * @vma - vma containing range to be munlock()ed.
 266 * @start - start address in @vma of the range
 267 * @end - end of range in @vma.
 268 *
 269 *  For mremap(), munmap() and exit().
 270 *
 271 * Called with @vma VM_LOCKED.
 272 *
 273 * Returns with VM_LOCKED cleared.  Callers must be prepared to
 274 * deal with this.
 275 *
 276 * We don't save and restore VM_LOCKED here because pages are
 277 * still on lru.  In unmap path, pages might be scanned by reclaim
 278 * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 279 * free them.  This will result in freeing mlocked pages.
 280 */
 281void munlock_vma_pages_range(struct vm_area_struct *vma,
 282                             unsigned long start, unsigned long end)
 283{
 284        unsigned long addr;
 285
 286        lru_add_drain();
 287        vma->vm_flags &= ~VM_LOCKED;
 288
 289        for (addr = start; addr < end; addr += PAGE_SIZE) {
 290                struct page *page;
 291                /*
 292                 * Although FOLL_DUMP is intended for get_dump_page(),
 293                 * it just so happens that its special treatment of the
 294                 * ZERO_PAGE (returning an error instead of doing get_page)
 295                 * suits munlock very well (and if somehow an abnormal page
 296                 * has sneaked into the range, we won't oops here: great).
 297                 */
 298                page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
 299                if (page && !IS_ERR(page)) {
 300                        lock_page(page);
 301                        /*
 302                         * Like in __mlock_vma_pages_range(),
 303                         * because we lock page here and migration is
 304                         * blocked by the elevated reference, we need
 305                         * only check for file-cache page truncation.
 306                         */
 307                        if (page->mapping)
 308                                munlock_vma_page(page);
 309                        unlock_page(page);
 310                        put_page(page);
 311                }
 312                cond_resched();
 313        }
 314}
 315
 316/*
 317 * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 318 *
 319 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 320 * munlock is a no-op.  However, for some special vmas, we go ahead and
 321 * populate the ptes via make_pages_present().
 322 *
 323 * For vmas that pass the filters, merge/split as appropriate.
 324 */
 325static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 326        unsigned long start, unsigned long end, unsigned int newflags)
 327{
 328        struct mm_struct *mm = vma->vm_mm;
 329        pgoff_t pgoff;
 330        int nr_pages;
 331        int ret = 0;
 332        int lock = newflags & VM_LOCKED;
 333
 334        if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
 335            is_vm_hugetlb_page(vma) || vma == get_gate_vma(current))
 336                goto out;       /* don't set VM_LOCKED,  don't count */
 337
 338        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 339        *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 340                          vma->vm_file, pgoff, vma_policy(vma));
 341        if (*prev) {
 342                vma = *prev;
 343                goto success;
 344        }
 345
 346        if (start != vma->vm_start) {
 347                ret = split_vma(mm, vma, start, 1);
 348                if (ret)
 349                        goto out;
 350        }
 351
 352        if (end != vma->vm_end) {
 353                ret = split_vma(mm, vma, end, 0);
 354                if (ret)
 355                        goto out;
 356        }
 357
 358success:
 359        /*
 360         * Keep track of amount of locked VM.
 361         */
 362        nr_pages = (end - start) >> PAGE_SHIFT;
 363        if (!lock)
 364                nr_pages = -nr_pages;
 365        mm->locked_vm += nr_pages;
 366
 367        /*
 368         * vm_flags is protected by the mmap_sem held in write mode.
 369         * It's okay if try_to_unmap_one unmaps a page just after we
 370         * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 371         */
 372
 373        if (lock)
 374                vma->vm_flags = newflags;
 375        else
 376                munlock_vma_pages_range(vma, start, end);
 377
 378out:
 379        *prev = vma;
 380        return ret;
 381}
 382
 383static int do_mlock(unsigned long start, size_t len, int on)
 384{
 385        unsigned long nstart, end, tmp;
 386        struct vm_area_struct * vma, * prev;
 387        int error;
 388
 389        VM_BUG_ON(start & ~PAGE_MASK);
 390        VM_BUG_ON(len != PAGE_ALIGN(len));
 391        end = start + len;
 392        if (end < start)
 393                return -EINVAL;
 394        if (end == start)
 395                return 0;
 396        vma = find_vma_prev(current->mm, start, &prev);
 397        if (!vma || vma->vm_start > start)
 398                return -ENOMEM;
 399
 400        if (start > vma->vm_start)
 401                prev = vma;
 402
 403        for (nstart = start ; ; ) {
 404                unsigned int newflags;
 405
 406                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 407
 408                newflags = vma->vm_flags | VM_LOCKED;
 409                if (!on)
 410                        newflags &= ~VM_LOCKED;
 411
 412                tmp = vma->vm_end;
 413                if (tmp > end)
 414                        tmp = end;
 415                error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 416                if (error)
 417                        break;
 418                nstart = tmp;
 419                if (nstart < prev->vm_end)
 420                        nstart = prev->vm_end;
 421                if (nstart >= end)
 422                        break;
 423
 424                vma = prev->vm_next;
 425                if (!vma || vma->vm_start != nstart) {
 426                        error = -ENOMEM;
 427                        break;
 428                }
 429        }
 430        return error;
 431}
 432
 433static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
 434{
 435        struct mm_struct *mm = current->mm;
 436        unsigned long end, nstart, nend;
 437        struct vm_area_struct *vma = NULL;
 438        int locked = 0;
 439        int ret = 0;
 440
 441        VM_BUG_ON(start & ~PAGE_MASK);
 442        VM_BUG_ON(len != PAGE_ALIGN(len));
 443        end = start + len;
 444
 445        for (nstart = start; nstart < end; nstart = nend) {
 446                /*
 447                 * We want to fault in pages for [nstart; end) address range.
 448                 * Find first corresponding VMA.
 449                 */
 450                if (!locked) {
 451                        locked = 1;
 452                        down_read(&mm->mmap_sem);
 453                        vma = find_vma(mm, nstart);
 454                } else if (nstart >= vma->vm_end)
 455                        vma = vma->vm_next;
 456                if (!vma || vma->vm_start >= end)
 457                        break;
 458                /*
 459                 * Set [nstart; nend) to intersection of desired address
 460                 * range with the first VMA. Also, skip undesirable VMA types.
 461                 */
 462                nend = min(end, vma->vm_end);
 463                if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 464                        continue;
 465                if (nstart < vma->vm_start)
 466                        nstart = vma->vm_start;
 467                /*
 468                 * Now fault in a range of pages. __mlock_vma_pages_range()
 469                 * double checks the vma flags, so that it won't mlock pages
 470                 * if the vma was already munlocked.
 471                 */
 472                ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
 473                if (ret < 0) {
 474                        if (ignore_errors) {
 475                                ret = 0;
 476                                continue;       /* continue at next VMA */
 477                        }
 478                        ret = __mlock_posix_error_return(ret);
 479                        break;
 480                }
 481                nend = nstart + ret * PAGE_SIZE;
 482                ret = 0;
 483        }
 484        if (locked)
 485                up_read(&mm->mmap_sem);
 486        return ret;     /* 0 or negative error code */
 487}
 488
 489SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 490{
 491        unsigned long locked;
 492        unsigned long lock_limit;
 493        int error = -ENOMEM;
 494
 495        if (!can_do_mlock())
 496                return -EPERM;
 497
 498        lru_add_drain_all();    /* flush pagevec */
 499
 500        down_write(&current->mm->mmap_sem);
 501        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 502        start &= PAGE_MASK;
 503
 504        locked = len >> PAGE_SHIFT;
 505        locked += current->mm->locked_vm;
 506
 507        lock_limit = rlimit(RLIMIT_MEMLOCK);
 508        lock_limit >>= PAGE_SHIFT;
 509
 510        /* check against resource limits */
 511        if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 512                error = do_mlock(start, len, 1);
 513        up_write(&current->mm->mmap_sem);
 514        if (!error)
 515                error = do_mlock_pages(start, len, 0);
 516        return error;
 517}
 518
 519SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 520{
 521        int ret;
 522
 523        down_write(&current->mm->mmap_sem);
 524        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 525        start &= PAGE_MASK;
 526        ret = do_mlock(start, len, 0);
 527        up_write(&current->mm->mmap_sem);
 528        return ret;
 529}
 530
 531static int do_mlockall(int flags)
 532{
 533        struct vm_area_struct * vma, * prev = NULL;
 534        unsigned int def_flags = 0;
 535
 536        if (flags & MCL_FUTURE)
 537                def_flags = VM_LOCKED;
 538        current->mm->def_flags = def_flags;
 539        if (flags == MCL_FUTURE)
 540                goto out;
 541
 542        for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 543                unsigned int newflags;
 544
 545                newflags = vma->vm_flags | VM_LOCKED;
 546                if (!(flags & MCL_CURRENT))
 547                        newflags &= ~VM_LOCKED;
 548
 549                /* Ignore errors */
 550                mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 551        }
 552out:
 553        return 0;
 554}
 555
 556SYSCALL_DEFINE1(mlockall, int, flags)
 557{
 558        unsigned long lock_limit;
 559        int ret = -EINVAL;
 560
 561        if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 562                goto out;
 563
 564        ret = -EPERM;
 565        if (!can_do_mlock())
 566                goto out;
 567
 568        lru_add_drain_all();    /* flush pagevec */
 569
 570        down_write(&current->mm->mmap_sem);
 571
 572        lock_limit = rlimit(RLIMIT_MEMLOCK);
 573        lock_limit >>= PAGE_SHIFT;
 574
 575        ret = -ENOMEM;
 576        if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 577            capable(CAP_IPC_LOCK))
 578                ret = do_mlockall(flags);
 579        up_write(&current->mm->mmap_sem);
 580        if (!ret && (flags & MCL_CURRENT)) {
 581                /* Ignore errors */
 582                do_mlock_pages(0, TASK_SIZE, 1);
 583        }
 584out:
 585        return ret;
 586}
 587
 588SYSCALL_DEFINE0(munlockall)
 589{
 590        int ret;
 591
 592        down_write(&current->mm->mmap_sem);
 593        ret = do_mlockall(0);
 594        up_write(&current->mm->mmap_sem);
 595        return ret;
 596}
 597
 598/*
 599 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 600 * shm segments) get accounted against the user_struct instead.
 601 */
 602static DEFINE_SPINLOCK(shmlock_user_lock);
 603
 604int user_shm_lock(size_t size, struct user_struct *user)
 605{
 606        unsigned long lock_limit, locked;
 607        int allowed = 0;
 608
 609        locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 610        lock_limit = rlimit(RLIMIT_MEMLOCK);
 611        if (lock_limit == RLIM_INFINITY)
 612                allowed = 1;
 613        lock_limit >>= PAGE_SHIFT;
 614        spin_lock(&shmlock_user_lock);
 615        if (!allowed &&
 616            locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 617                goto out;
 618        get_uid(user);
 619        user->locked_shm += locked;
 620        allowed = 1;
 621out:
 622        spin_unlock(&shmlock_user_lock);
 623        return allowed;
 624}
 625
 626void user_shm_unlock(size_t size, struct user_struct *user)
 627{
 628        spin_lock(&shmlock_user_lock);
 629        user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 630        spin_unlock(&shmlock_user_lock);
 631        free_uid(user);
 632}
 633