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        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 */
  77void mlock_vma_page(struct page *page)
  78{
  79        BUG_ON(!PageLocked(page));
  80
  81        if (!TestSetPageMlocked(page)) {
  82                mod_zone_page_state(page_zone(page), NR_MLOCK,
  83                                    hpage_nr_pages(page));
  84                count_vm_event(UNEVICTABLE_PGMLOCKED);
  85                if (!isolate_lru_page(page))
  86                        putback_lru_page(page);
  87        }
  88}
  89
  90/**
  91 * munlock_vma_page - munlock a vma page
  92 * @page - page to be unlocked
  93 *
  94 * called from munlock()/munmap() path with page supposedly on the LRU.
  95 * When we munlock a page, because the vma where we found the page is being
  96 * munlock()ed or munmap()ed, we want to check whether other vmas hold the
  97 * page locked so that we can leave it on the unevictable lru list and not
  98 * bother vmscan with it.  However, to walk the page's rmap list in
  99 * try_to_munlock() we must isolate the page from the LRU.  If some other
 100 * task has removed the page from the LRU, we won't be able to do that.
 101 * So we clear the PageMlocked as we might not get another chance.  If we
 102 * can't isolate the page, we leave it for putback_lru_page() and vmscan
 103 * [page_referenced()/try_to_unmap()] to deal with.
 104 */
 105unsigned int munlock_vma_page(struct page *page)
 106{
 107        unsigned int page_mask = 0;
 108
 109        BUG_ON(!PageLocked(page));
 110
 111        if (TestClearPageMlocked(page)) {
 112                unsigned int nr_pages = hpage_nr_pages(page);
 113                mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
 114                page_mask = nr_pages - 1;
 115                if (!isolate_lru_page(page)) {
 116                        int ret = SWAP_AGAIN;
 117
 118                        /*
 119                         * Optimization: if the page was mapped just once,
 120                         * that's our mapping and we don't need to check all the
 121                         * other vmas.
 122                         */
 123                        if (page_mapcount(page) > 1)
 124                                ret = try_to_munlock(page);
 125                        /*
 126                         * did try_to_unlock() succeed or punt?
 127                         */
 128                        if (ret != SWAP_MLOCK)
 129                                count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 130
 131                        putback_lru_page(page);
 132                } else {
 133                        /*
 134                         * Some other task has removed the page from the LRU.
 135                         * putback_lru_page() will take care of removing the
 136                         * page from the unevictable list, if necessary.
 137                         * vmscan [page_referenced()] will move the page back
 138                         * to the unevictable list if some other vma has it
 139                         * mlocked.
 140                         */
 141                        if (PageUnevictable(page))
 142                                count_vm_event(UNEVICTABLE_PGSTRANDED);
 143                        else
 144                                count_vm_event(UNEVICTABLE_PGMUNLOCKED);
 145                }
 146        }
 147
 148        return page_mask;
 149}
 150
 151/**
 152 * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
 153 * @vma:   target vma
 154 * @start: start address
 155 * @end:   end address
 156 *
 157 * This takes care of making the pages present too.
 158 *
 159 * return 0 on success, negative error code on error.
 160 *
 161 * vma->vm_mm->mmap_sem must be held for at least read.
 162 */
 163long __mlock_vma_pages_range(struct vm_area_struct *vma,
 164                unsigned long start, unsigned long end, int *nonblocking)
 165{
 166        struct mm_struct *mm = vma->vm_mm;
 167        unsigned long nr_pages = (end - start) / PAGE_SIZE;
 168        int gup_flags;
 169
 170        VM_BUG_ON(start & ~PAGE_MASK);
 171        VM_BUG_ON(end   & ~PAGE_MASK);
 172        VM_BUG_ON(start < vma->vm_start);
 173        VM_BUG_ON(end   > vma->vm_end);
 174        VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
 175
 176        gup_flags = FOLL_TOUCH | FOLL_MLOCK;
 177        /*
 178         * We want to touch writable mappings with a write fault in order
 179         * to break COW, except for shared mappings because these don't COW
 180         * and we would not want to dirty them for nothing.
 181         */
 182        if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
 183                gup_flags |= FOLL_WRITE;
 184
 185        /*
 186         * We want mlock to succeed for regions that have any permissions
 187         * other than PROT_NONE.
 188         */
 189        if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
 190                gup_flags |= FOLL_FORCE;
 191
 192        /*
 193         * We made sure addr is within a VMA, so the following will
 194         * not result in a stack expansion that recurses back here.
 195         */
 196        return __get_user_pages(current, mm, start, nr_pages, gup_flags,
 197                                NULL, NULL, nonblocking);
 198}
 199
 200/*
 201 * convert get_user_pages() return value to posix mlock() error
 202 */
 203static int __mlock_posix_error_return(long retval)
 204{
 205        if (retval == -EFAULT)
 206                retval = -ENOMEM;
 207        else if (retval == -ENOMEM)
 208                retval = -EAGAIN;
 209        return retval;
 210}
 211
 212/*
 213 * munlock_vma_pages_range() - munlock all pages in the vma range.'
 214 * @vma - vma containing range to be munlock()ed.
 215 * @start - start address in @vma of the range
 216 * @end - end of range in @vma.
 217 *
 218 *  For mremap(), munmap() and exit().
 219 *
 220 * Called with @vma VM_LOCKED.
 221 *
 222 * Returns with VM_LOCKED cleared.  Callers must be prepared to
 223 * deal with this.
 224 *
 225 * We don't save and restore VM_LOCKED here because pages are
 226 * still on lru.  In unmap path, pages might be scanned by reclaim
 227 * and re-mlocked by try_to_{munlock|unmap} before we unmap and
 228 * free them.  This will result in freeing mlocked pages.
 229 */
 230void munlock_vma_pages_range(struct vm_area_struct *vma,
 231                             unsigned long start, unsigned long end)
 232{
 233        vma->vm_flags &= ~VM_LOCKED;
 234
 235        while (start < end) {
 236                struct page *page;
 237                unsigned int page_mask, page_increm;
 238
 239                /*
 240                 * Although FOLL_DUMP is intended for get_dump_page(),
 241                 * it just so happens that its special treatment of the
 242                 * ZERO_PAGE (returning an error instead of doing get_page)
 243                 * suits munlock very well (and if somehow an abnormal page
 244                 * has sneaked into the range, we won't oops here: great).
 245                 */
 246                page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
 247                                        &page_mask);
 248                if (page && !IS_ERR(page)) {
 249                        lock_page(page);
 250                        lru_add_drain();
 251                        /*
 252                         * Any THP page found by follow_page_mask() may have
 253                         * gotten split before reaching munlock_vma_page(),
 254                         * so we need to recompute the page_mask here.
 255                         */
 256                        page_mask = munlock_vma_page(page);
 257                        unlock_page(page);
 258                        put_page(page);
 259                }
 260                page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
 261                start += page_increm * PAGE_SIZE;
 262                cond_resched();
 263        }
 264}
 265
 266/*
 267 * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 268 *
 269 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 270 * munlock is a no-op.  However, for some special vmas, we go ahead and
 271 * populate the ptes.
 272 *
 273 * For vmas that pass the filters, merge/split as appropriate.
 274 */
 275static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 276        unsigned long start, unsigned long end, vm_flags_t newflags)
 277{
 278        struct mm_struct *mm = vma->vm_mm;
 279        pgoff_t pgoff;
 280        int nr_pages;
 281        int ret = 0;
 282        int lock = !!(newflags & VM_LOCKED);
 283
 284        if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
 285            is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
 286                goto out;       /* don't set VM_LOCKED,  don't count */
 287
 288        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 289        *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 290                          vma->vm_file, pgoff, vma_policy(vma));
 291        if (*prev) {
 292                vma = *prev;
 293                goto success;
 294        }
 295
 296        if (start != vma->vm_start) {
 297                ret = split_vma(mm, vma, start, 1);
 298                if (ret)
 299                        goto out;
 300        }
 301
 302        if (end != vma->vm_end) {
 303                ret = split_vma(mm, vma, end, 0);
 304                if (ret)
 305                        goto out;
 306        }
 307
 308success:
 309        /*
 310         * Keep track of amount of locked VM.
 311         */
 312        nr_pages = (end - start) >> PAGE_SHIFT;
 313        if (!lock)
 314                nr_pages = -nr_pages;
 315        mm->locked_vm += nr_pages;
 316
 317        /*
 318         * vm_flags is protected by the mmap_sem held in write mode.
 319         * It's okay if try_to_unmap_one unmaps a page just after we
 320         * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 321         */
 322
 323        if (lock)
 324                vma->vm_flags = newflags;
 325        else
 326                munlock_vma_pages_range(vma, start, end);
 327
 328out:
 329        *prev = vma;
 330        return ret;
 331}
 332
 333static int do_mlock(unsigned long start, size_t len, int on)
 334{
 335        unsigned long nstart, end, tmp;
 336        struct vm_area_struct * vma, * prev;
 337        int error;
 338
 339        VM_BUG_ON(start & ~PAGE_MASK);
 340        VM_BUG_ON(len != PAGE_ALIGN(len));
 341        end = start + len;
 342        if (end < start)
 343                return -EINVAL;
 344        if (end == start)
 345                return 0;
 346        vma = find_vma(current->mm, start);
 347        if (!vma || vma->vm_start > start)
 348                return -ENOMEM;
 349
 350        prev = vma->vm_prev;
 351        if (start > vma->vm_start)
 352                prev = vma;
 353
 354        for (nstart = start ; ; ) {
 355                vm_flags_t newflags;
 356
 357                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 358
 359                newflags = vma->vm_flags & ~VM_LOCKED;
 360                if (on)
 361                        newflags |= VM_LOCKED;
 362
 363                tmp = vma->vm_end;
 364                if (tmp > end)
 365                        tmp = end;
 366                error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 367                if (error)
 368                        break;
 369                nstart = tmp;
 370                if (nstart < prev->vm_end)
 371                        nstart = prev->vm_end;
 372                if (nstart >= end)
 373                        break;
 374
 375                vma = prev->vm_next;
 376                if (!vma || vma->vm_start != nstart) {
 377                        error = -ENOMEM;
 378                        break;
 379                }
 380        }
 381        return error;
 382}
 383
 384/*
 385 * __mm_populate - populate and/or mlock pages within a range of address space.
 386 *
 387 * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
 388 * flags. VMAs must be already marked with the desired vm_flags, and
 389 * mmap_sem must not be held.
 390 */
 391int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
 392{
 393        struct mm_struct *mm = current->mm;
 394        unsigned long end, nstart, nend;
 395        struct vm_area_struct *vma = NULL;
 396        int locked = 0;
 397        long ret = 0;
 398
 399        VM_BUG_ON(start & ~PAGE_MASK);
 400        VM_BUG_ON(len != PAGE_ALIGN(len));
 401        end = start + len;
 402
 403        for (nstart = start; nstart < end; nstart = nend) {
 404                /*
 405                 * We want to fault in pages for [nstart; end) address range.
 406                 * Find first corresponding VMA.
 407                 */
 408                if (!locked) {
 409                        locked = 1;
 410                        down_read(&mm->mmap_sem);
 411                        vma = find_vma(mm, nstart);
 412                } else if (nstart >= vma->vm_end)
 413                        vma = vma->vm_next;
 414                if (!vma || vma->vm_start >= end)
 415                        break;
 416                /*
 417                 * Set [nstart; nend) to intersection of desired address
 418                 * range with the first VMA. Also, skip undesirable VMA types.
 419                 */
 420                nend = min(end, vma->vm_end);
 421                if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 422                        continue;
 423                if (nstart < vma->vm_start)
 424                        nstart = vma->vm_start;
 425                /*
 426                 * Now fault in a range of pages. __mlock_vma_pages_range()
 427                 * double checks the vma flags, so that it won't mlock pages
 428                 * if the vma was already munlocked.
 429                 */
 430                ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
 431                if (ret < 0) {
 432                        if (ignore_errors) {
 433                                ret = 0;
 434                                continue;       /* continue at next VMA */
 435                        }
 436                        ret = __mlock_posix_error_return(ret);
 437                        break;
 438                }
 439                nend = nstart + ret * PAGE_SIZE;
 440                ret = 0;
 441        }
 442        if (locked)
 443                up_read(&mm->mmap_sem);
 444        return ret;     /* 0 or negative error code */
 445}
 446
 447SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 448{
 449        unsigned long locked;
 450        unsigned long lock_limit;
 451        int error = -ENOMEM;
 452
 453        if (!can_do_mlock())
 454                return -EPERM;
 455
 456        lru_add_drain_all();    /* flush pagevec */
 457
 458        down_write(&current->mm->mmap_sem);
 459        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 460        start &= PAGE_MASK;
 461
 462        locked = len >> PAGE_SHIFT;
 463        locked += current->mm->locked_vm;
 464
 465        lock_limit = rlimit(RLIMIT_MEMLOCK);
 466        lock_limit >>= PAGE_SHIFT;
 467
 468        /* check against resource limits */
 469        if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 470                error = do_mlock(start, len, 1);
 471        up_write(&current->mm->mmap_sem);
 472        if (!error)
 473                error = __mm_populate(start, len, 0);
 474        return error;
 475}
 476
 477SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 478{
 479        int ret;
 480
 481        down_write(&current->mm->mmap_sem);
 482        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 483        start &= PAGE_MASK;
 484        ret = do_mlock(start, len, 0);
 485        up_write(&current->mm->mmap_sem);
 486        return ret;
 487}
 488
 489static int do_mlockall(int flags)
 490{
 491        struct vm_area_struct * vma, * prev = NULL;
 492
 493        if (flags & MCL_FUTURE)
 494                current->mm->def_flags |= VM_LOCKED;
 495        else
 496                current->mm->def_flags &= ~VM_LOCKED;
 497        if (flags == MCL_FUTURE)
 498                goto out;
 499
 500        for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 501                vm_flags_t newflags;
 502
 503                newflags = vma->vm_flags & ~VM_LOCKED;
 504                if (flags & MCL_CURRENT)
 505                        newflags |= VM_LOCKED;
 506
 507                /* Ignore errors */
 508                mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 509        }
 510out:
 511        return 0;
 512}
 513
 514SYSCALL_DEFINE1(mlockall, int, flags)
 515{
 516        unsigned long lock_limit;
 517        int ret = -EINVAL;
 518
 519        if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 520                goto out;
 521
 522        ret = -EPERM;
 523        if (!can_do_mlock())
 524                goto out;
 525
 526        if (flags & MCL_CURRENT)
 527                lru_add_drain_all();    /* flush pagevec */
 528
 529        down_write(&current->mm->mmap_sem);
 530
 531        lock_limit = rlimit(RLIMIT_MEMLOCK);
 532        lock_limit >>= PAGE_SHIFT;
 533
 534        ret = -ENOMEM;
 535        if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 536            capable(CAP_IPC_LOCK))
 537                ret = do_mlockall(flags);
 538        up_write(&current->mm->mmap_sem);
 539        if (!ret && (flags & MCL_CURRENT))
 540                mm_populate(0, TASK_SIZE);
 541out:
 542        return ret;
 543}
 544
 545SYSCALL_DEFINE0(munlockall)
 546{
 547        int ret;
 548
 549        down_write(&current->mm->mmap_sem);
 550        ret = do_mlockall(0);
 551        up_write(&current->mm->mmap_sem);
 552        return ret;
 553}
 554
 555/*
 556 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 557 * shm segments) get accounted against the user_struct instead.
 558 */
 559static DEFINE_SPINLOCK(shmlock_user_lock);
 560
 561int user_shm_lock(size_t size, struct user_struct *user)
 562{
 563        unsigned long lock_limit, locked;
 564        int allowed = 0;
 565
 566        locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 567        lock_limit = rlimit(RLIMIT_MEMLOCK);
 568        if (lock_limit == RLIM_INFINITY)
 569                allowed = 1;
 570        lock_limit >>= PAGE_SHIFT;
 571        spin_lock(&shmlock_user_lock);
 572        if (!allowed &&
 573            locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 574                goto out;
 575        get_uid(user);
 576        user->locked_shm += locked;
 577        allowed = 1;
 578out:
 579        spin_unlock(&shmlock_user_lock);
 580        return allowed;
 581}
 582
 583void user_shm_unlock(size_t size, struct user_struct *user)
 584{
 585        spin_lock(&shmlock_user_lock);
 586        user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 587        spin_unlock(&shmlock_user_lock);
 588        free_uid(user);
 589}
 590
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