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/export.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 = SWAP_AGAIN;
 114
 115                        /*
 116                         * Optimization: if the page was mapped just once,
 117                         * that's our mapping and we don't need to check all the
 118                         * other vmas.
 119                         */
 120                        if (page_mapcount(page) > 1)
 121                                ret = try_to_munlock(page);
 122                        /*
 123                         * did try_to_unlock() succeed or punt?
 124                         */
 125                        if (ret != SWAP_MLOCK)
 126                                count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 127
 128                        putback_lru_page(page);
 129                } else {
 130                        /*
 131                         * Some other task has removed the page from the LRU.
 132                         * putback_lru_page() will take care of removing the
 133                         * page from the unevictable list, if necessary.
 134                         * vmscan [page_referenced()] will move the page back
 135                         * to the unevictable list if some other vma has it
 136                         * mlocked.
 137                         */
 138                        if (PageUnevictable(page))
 139                                count_vm_event(UNEVICTABLE_PGSTRANDED);
 140                        else
 141                                count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 142                }
 143        }
 144}
 145
 146/**
 147 * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
 148 * @vma:   target vma
 149 * @start: start address
 150 * @end:   end address
 151 *
 152 * This takes care of making the pages present too.
 153 *
 154 * return 0 on success, negative error code on error.
 155 *
 156 * vma->vm_mm->mmap_sem must be held for at least read.
 157 */
 158static long __mlock_vma_pages_range(struct vm_area_struct *vma,
 159                                    unsigned long start, unsigned long end,
 160                                    int *nonblocking)
 161{
 162        struct mm_struct *mm = vma->vm_mm;
 163        unsigned long addr = start;
 164        int nr_pages = (end - start) / PAGE_SIZE;
 165        int gup_flags;
 166
 167        VM_BUG_ON(start & ~PAGE_MASK);
 168        VM_BUG_ON(end   & ~PAGE_MASK);
 169        VM_BUG_ON(start < vma->vm_start);
 170        VM_BUG_ON(end   > vma->vm_end);
 171        VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 172
 173        gup_flags = FOLL_TOUCH | FOLL_MLOCK;
 174        /*
 175         * We want to touch writable mappings with a write fault in order
 176         * to break COW, except for shared mappings because these don't COW
 177         * and we would not want to dirty them for nothing.
 178         */
 179        if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
 180                gup_flags |= FOLL_WRITE;
 181
 182        /*
 183         * We want mlock to succeed for regions that have any permissions
 184         * other than PROT_NONE.
 185         */
 186        if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
 187                gup_flags |= FOLL_FORCE;
 188
 189        return __get_user_pages(current, mm, addr, nr_pages, gup_flags,
 190                                NULL, NULL, nonblocking);
 191}
 192
 193/*
 194 * convert get_user_pages() return value to posix mlock() error
 195 */
 196static int __mlock_posix_error_return(long retval)
 197{
 198        if (retval == -EFAULT)
 199                retval = -ENOMEM;
 200        else if (retval == -ENOMEM)
 201                retval = -EAGAIN;
 202        return retval;
 203}
 204
 205/**
 206 * mlock_vma_pages_range() - mlock pages in specified vma range.
 207 * @vma - the vma containing the specfied address range
 208 * @start - starting address in @vma to mlock
 209 * @end   - end address [+1] in @vma to mlock
 210 *
 211 * For mmap()/mremap()/expansion of mlocked vma.
 212 *
 213 * return 0 on success for "normal" vmas.
 214 *
 215 * return number of pages [> 0] to be removed from locked_vm on success
 216 * of "special" vmas.
 217 */
 218long mlock_vma_pages_range(struct vm_area_struct *vma,
 219                        unsigned long start, unsigned long end)
 220{
 221        int nr_pages = (end - start) / PAGE_SIZE;
 222        BUG_ON(!(vma->vm_flags & VM_LOCKED));
 223
 224        /*
 225         * filter unlockable vmas
 226         */
 227        if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 228                goto no_mlock;
 229
 230        if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 231                        is_vm_hugetlb_page(vma) ||
 232                        vma == get_gate_vma(current->mm))) {
 233
 234                __mlock_vma_pages_range(vma, start, end, NULL);
 235
 236                /* Hide errors from mmap() and other callers */
 237                return 0;
 238        }
 239
 240        /*
 241         * User mapped kernel pages or huge pages:
 242         * make these pages present to populate the ptes, but
 243         * fall thru' to reset VM_LOCKED--no need to unlock, and
 244         * return nr_pages so these don't get counted against task's
 245         * locked limit.  huge pages are already counted against
 246         * locked vm limit.
 247         */
 248        make_pages_present(start, end);
 249
 250no_mlock:
 251        vma->vm_flags &= ~VM_LOCKED;    /* and don't come back! */
 252        return nr_pages;                /* error or pages NOT mlocked */
 253}
 254
 255/*
 256 * munlock_vma_pages_range() - munlock all pages in the vma range.'
 257 * @vma - vma containing range to be munlock()ed.
 258 * @start - start address in @vma of the range
 259 * @end - end of range in @vma.
 260 *
 261 *  For mremap(), munmap() and exit().
 262 *
 263 * Called with @vma VM_LOCKED.
 264 *
 265 * Returns with VM_LOCKED cleared.  Callers must be prepared to
 266 * deal with this.
 267 *
 268 * We don't save and restore VM_LOCKED here because pages are
 269 * still on lru.  In unmap path, pages might be scanned by reclaim
 270 * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 271 * free them.  This will result in freeing mlocked pages.
 272 */
 273void munlock_vma_pages_range(struct vm_area_struct *vma,
 274                             unsigned long start, unsigned long end)
 275{
 276        unsigned long addr;
 277
 278        lru_add_drain();
 279        vma->vm_flags &= ~VM_LOCKED;
 280
 281        for (addr = start; addr < end; addr += PAGE_SIZE) {
 282                struct page *page;
 283                /*
 284                 * Although FOLL_DUMP is intended for get_dump_page(),
 285                 * it just so happens that its special treatment of the
 286                 * ZERO_PAGE (returning an error instead of doing get_page)
 287                 * suits munlock very well (and if somehow an abnormal page
 288                 * has sneaked into the range, we won't oops here: great).
 289                 */
 290                page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
 291                if (page && !IS_ERR(page)) {
 292                        lock_page(page);
 293                        /*
 294                         * Like in __mlock_vma_pages_range(),
 295                         * because we lock page here and migration is
 296                         * blocked by the elevated reference, we need
 297                         * only check for file-cache page truncation.
 298                         */
 299                        if (page->mapping)
 300                                munlock_vma_page(page);
 301                        unlock_page(page);
 302                        put_page(page);
 303                }
 304                cond_resched();
 305        }
 306}
 307
 308/*
 309 * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 310 *
 311 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 312 * munlock is a no-op.  However, for some special vmas, we go ahead and
 313 * populate the ptes via make_pages_present().
 314 *
 315 * For vmas that pass the filters, merge/split as appropriate.
 316 */
 317static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 318        unsigned long start, unsigned long end, vm_flags_t newflags)
 319{
 320        struct mm_struct *mm = vma->vm_mm;
 321        pgoff_t pgoff;
 322        int nr_pages;
 323        int ret = 0;
 324        int lock = !!(newflags & VM_LOCKED);
 325
 326        if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
 327            is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
 328                goto out;       /* don't set VM_LOCKED,  don't count */
 329
 330        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 331        *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 332                          vma->vm_file, pgoff, vma_policy(vma));
 333        if (*prev) {
 334                vma = *prev;
 335                goto success;
 336        }
 337
 338        if (start != vma->vm_start) {
 339                ret = split_vma(mm, vma, start, 1);
 340                if (ret)
 341                        goto out;
 342        }
 343
 344        if (end != vma->vm_end) {
 345                ret = split_vma(mm, vma, end, 0);
 346                if (ret)
 347                        goto out;
 348        }
 349
 350success:
 351        /*
 352         * Keep track of amount of locked VM.
 353         */
 354        nr_pages = (end - start) >> PAGE_SHIFT;
 355        if (!lock)
 356                nr_pages = -nr_pages;
 357        mm->locked_vm += nr_pages;
 358
 359        /*
 360         * vm_flags is protected by the mmap_sem held in write mode.
 361         * It's okay if try_to_unmap_one unmaps a page just after we
 362         * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 363         */
 364
 365        if (lock)
 366                vma->vm_flags = newflags;
 367        else
 368                munlock_vma_pages_range(vma, start, end);
 369
 370out:
 371        *prev = vma;
 372        return ret;
 373}
 374
 375static int do_mlock(unsigned long start, size_t len, int on)
 376{
 377        unsigned long nstart, end, tmp;
 378        struct vm_area_struct * vma, * prev;
 379        int error;
 380
 381        VM_BUG_ON(start & ~PAGE_MASK);
 382        VM_BUG_ON(len != PAGE_ALIGN(len));
 383        end = start + len;
 384        if (end < start)
 385                return -EINVAL;
 386        if (end == start)
 387                return 0;
 388        vma = find_vma(current->mm, start);
 389        if (!vma || vma->vm_start > start)
 390                return -ENOMEM;
 391
 392        prev = vma->vm_prev;
 393        if (start > vma->vm_start)
 394                prev = vma;
 395
 396        for (nstart = start ; ; ) {
 397                vm_flags_t newflags;
 398
 399                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 400
 401                newflags = vma->vm_flags | VM_LOCKED;
 402                if (!on)
 403                        newflags &= ~VM_LOCKED;
 404
 405                tmp = vma->vm_end;
 406                if (tmp > end)
 407                        tmp = end;
 408                error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 409                if (error)
 410                        break;
 411                nstart = tmp;
 412                if (nstart < prev->vm_end)
 413                        nstart = prev->vm_end;
 414                if (nstart >= end)
 415                        break;
 416
 417                vma = prev->vm_next;
 418                if (!vma || vma->vm_start != nstart) {
 419                        error = -ENOMEM;
 420                        break;
 421                }
 422        }
 423        return error;
 424}
 425
 426static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
 427{
 428        struct mm_struct *mm = current->mm;
 429        unsigned long end, nstart, nend;
 430        struct vm_area_struct *vma = NULL;
 431        int locked = 0;
 432        int ret = 0;
 433
 434        VM_BUG_ON(start & ~PAGE_MASK);
 435        VM_BUG_ON(len != PAGE_ALIGN(len));
 436        end = start + len;
 437
 438        for (nstart = start; nstart < end; nstart = nend) {
 439                /*
 440                 * We want to fault in pages for [nstart; end) address range.
 441                 * Find first corresponding VMA.
 442                 */
 443                if (!locked) {
 444                        locked = 1;
 445                        down_read(&mm->mmap_sem);
 446                        vma = find_vma(mm, nstart);
 447                } else if (nstart >= vma->vm_end)
 448                        vma = vma->vm_next;
 449                if (!vma || vma->vm_start >= end)
 450                        break;
 451                /*
 452                 * Set [nstart; nend) to intersection of desired address
 453                 * range with the first VMA. Also, skip undesirable VMA types.
 454                 */
 455                nend = min(end, vma->vm_end);
 456                if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 457                        continue;
 458                if (nstart < vma->vm_start)
 459                        nstart = vma->vm_start;
 460                /*
 461                 * Now fault in a range of pages. __mlock_vma_pages_range()
 462                 * double checks the vma flags, so that it won't mlock pages
 463                 * if the vma was already munlocked.
 464                 */
 465                ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
 466                if (ret < 0) {
 467                        if (ignore_errors) {
 468                                ret = 0;
 469                                continue;       /* continue at next VMA */
 470                        }
 471                        ret = __mlock_posix_error_return(ret);
 472                        break;
 473                }
 474                nend = nstart + ret * PAGE_SIZE;
 475                ret = 0;
 476        }
 477        if (locked)
 478                up_read(&mm->mmap_sem);
 479        return ret;     /* 0 or negative error code */
 480}
 481
 482SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 483{
 484        unsigned long locked;
 485        unsigned long lock_limit;
 486        int error = -ENOMEM;
 487
 488        if (!can_do_mlock())
 489                return -EPERM;
 490
 491        lru_add_drain_all();    /* flush pagevec */
 492
 493        down_write(&current->mm->mmap_sem);
 494        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 495        start &= PAGE_MASK;
 496
 497        locked = len >> PAGE_SHIFT;
 498        locked += current->mm->locked_vm;
 499
 500        lock_limit = rlimit(RLIMIT_MEMLOCK);
 501        lock_limit >>= PAGE_SHIFT;
 502
 503        /* check against resource limits */
 504        if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 505                error = do_mlock(start, len, 1);
 506        up_write(&current->mm->mmap_sem);
 507        if (!error)
 508                error = do_mlock_pages(start, len, 0);
 509        return error;
 510}
 511
 512SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 513{
 514        int ret;
 515
 516        down_write(&current->mm->mmap_sem);
 517        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 518        start &= PAGE_MASK;
 519        ret = do_mlock(start, len, 0);
 520        up_write(&current->mm->mmap_sem);
 521        return ret;
 522}
 523
 524static int do_mlockall(int flags)
 525{
 526        struct vm_area_struct * vma, * prev = NULL;
 527        unsigned int def_flags = 0;
 528
 529        if (flags & MCL_FUTURE)
 530                def_flags = VM_LOCKED;
 531        current->mm->def_flags = def_flags;
 532        if (flags == MCL_FUTURE)
 533                goto out;
 534
 535        for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 536                vm_flags_t newflags;
 537
 538                newflags = vma->vm_flags | VM_LOCKED;
 539                if (!(flags & MCL_CURRENT))
 540                        newflags &= ~VM_LOCKED;
 541
 542                /* Ignore errors */
 543                mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 544        }
 545out:
 546        return 0;
 547}
 548
 549SYSCALL_DEFINE1(mlockall, int, flags)
 550{
 551        unsigned long lock_limit;
 552        int ret = -EINVAL;
 553
 554        if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 555                goto out;
 556
 557        ret = -EPERM;
 558        if (!can_do_mlock())
 559                goto out;
 560
 561        if (flags & MCL_CURRENT)
 562                lru_add_drain_all();    /* flush pagevec */
 563
 564        down_write(&current->mm->mmap_sem);
 565
 566        lock_limit = rlimit(RLIMIT_MEMLOCK);
 567        lock_limit >>= PAGE_SHIFT;
 568
 569        ret = -ENOMEM;
 570        if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 571            capable(CAP_IPC_LOCK))
 572                ret = do_mlockall(flags);
 573        up_write(&current->mm->mmap_sem);
 574        if (!ret && (flags & MCL_CURRENT)) {
 575                /* Ignore errors */
 576                do_mlock_pages(0, TASK_SIZE, 1);
 577        }
 578out:
 579        return ret;
 580}
 581
 582SYSCALL_DEFINE0(munlockall)
 583{
 584        int ret;
 585
 586        down_write(&current->mm->mmap_sem);
 587        ret = do_mlockall(0);
 588        up_write(&current->mm->mmap_sem);
 589        return ret;
 590}
 591
 592/*
 593 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 594 * shm segments) get accounted against the user_struct instead.
 595 */
 596static DEFINE_SPINLOCK(shmlock_user_lock);
 597
 598int user_shm_lock(size_t size, struct user_struct *user)
 599{
 600        unsigned long lock_limit, locked;
 601        int allowed = 0;
 602
 603        locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 604        lock_limit = rlimit(RLIMIT_MEMLOCK);
 605        if (lock_limit == RLIM_INFINITY)
 606                allowed = 1;
 607        lock_limit >>= PAGE_SHIFT;
 608        spin_lock(&shmlock_user_lock);
 609        if (!allowed &&
 610            locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 611                goto out;
 612        get_uid(user);
 613        user->locked_shm += locked;
 614        allowed = 1;
 615out:
 616        spin_unlock(&shmlock_user_lock);
 617        return allowed;
 618}
 619
 620void user_shm_unlock(size_t size, struct user_struct *user)
 621{
 622        spin_lock(&shmlock_user_lock);
 623        user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 624        spin_unlock(&shmlock_user_lock);
 625        free_uid(user);
 626}
 627
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