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 */
 105void munlock_vma_page(struct page *page)
 106{
 107        BUG_ON(!PageLocked(page));
 108
 109        if (TestClearPageMlocked(page)) {
 110                mod_zone_page_state(page_zone(page), NR_MLOCK,
 111                                    -hpage_nr_pages(page));
 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) ||
 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                        munlock_vma_page(page);
 294                        unlock_page(page);
 295                        put_page(page);
 296                }
 297                cond_resched();
 298        }
 299}
 300
 301/*
 302 * mlock_fixup  - handle mlock[all]/munlock[all] requests.
 303 *
 304 * Filters out "special" vmas -- VM_LOCKED never gets set for these, and
 305 * munlock is a no-op.  However, for some special vmas, we go ahead and
 306 * populate the ptes via make_pages_present().
 307 *
 308 * For vmas that pass the filters, merge/split as appropriate.
 309 */
 310static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 311        unsigned long start, unsigned long end, vm_flags_t newflags)
 312{
 313        struct mm_struct *mm = vma->vm_mm;
 314        pgoff_t pgoff;
 315        int nr_pages;
 316        int ret = 0;
 317        int lock = !!(newflags & VM_LOCKED);
 318
 319        if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
 320            is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
 321                goto out;       /* don't set VM_LOCKED,  don't count */
 322
 323        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 324        *prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
 325                          vma->vm_file, pgoff, vma_policy(vma));
 326        if (*prev) {
 327                vma = *prev;
 328                goto success;
 329        }
 330
 331        if (start != vma->vm_start) {
 332                ret = split_vma(mm, vma, start, 1);
 333                if (ret)
 334                        goto out;
 335        }
 336
 337        if (end != vma->vm_end) {
 338                ret = split_vma(mm, vma, end, 0);
 339                if (ret)
 340                        goto out;
 341        }
 342
 343success:
 344        /*
 345         * Keep track of amount of locked VM.
 346         */
 347        nr_pages = (end - start) >> PAGE_SHIFT;
 348        if (!lock)
 349                nr_pages = -nr_pages;
 350        mm->locked_vm += nr_pages;
 351
 352        /*
 353         * vm_flags is protected by the mmap_sem held in write mode.
 354         * It's okay if try_to_unmap_one unmaps a page just after we
 355         * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
 356         */
 357
 358        if (lock)
 359                vma->vm_flags = newflags;
 360        else
 361                munlock_vma_pages_range(vma, start, end);
 362
 363out:
 364        *prev = vma;
 365        return ret;
 366}
 367
 368static int do_mlock(unsigned long start, size_t len, int on)
 369{
 370        unsigned long nstart, end, tmp;
 371        struct vm_area_struct * vma, * prev;
 372        int error;
 373
 374        VM_BUG_ON(start & ~PAGE_MASK);
 375        VM_BUG_ON(len != PAGE_ALIGN(len));
 376        end = start + len;
 377        if (end < start)
 378                return -EINVAL;
 379        if (end == start)
 380                return 0;
 381        vma = find_vma(current->mm, start);
 382        if (!vma || vma->vm_start > start)
 383                return -ENOMEM;
 384
 385        prev = vma->vm_prev;
 386        if (start > vma->vm_start)
 387                prev = vma;
 388
 389        for (nstart = start ; ; ) {
 390                vm_flags_t newflags;
 391
 392                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 393
 394                newflags = vma->vm_flags | VM_LOCKED;
 395                if (!on)
 396                        newflags &= ~VM_LOCKED;
 397
 398                tmp = vma->vm_end;
 399                if (tmp > end)
 400                        tmp = end;
 401                error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
 402                if (error)
 403                        break;
 404                nstart = tmp;
 405                if (nstart < prev->vm_end)
 406                        nstart = prev->vm_end;
 407                if (nstart >= end)
 408                        break;
 409
 410                vma = prev->vm_next;
 411                if (!vma || vma->vm_start != nstart) {
 412                        error = -ENOMEM;
 413                        break;
 414                }
 415        }
 416        return error;
 417}
 418
 419static int do_mlock_pages(unsigned long start, size_t len, int ignore_errors)
 420{
 421        struct mm_struct *mm = current->mm;
 422        unsigned long end, nstart, nend;
 423        struct vm_area_struct *vma = NULL;
 424        int locked = 0;
 425        int ret = 0;
 426
 427        VM_BUG_ON(start & ~PAGE_MASK);
 428        VM_BUG_ON(len != PAGE_ALIGN(len));
 429        end = start + len;
 430
 431        for (nstart = start; nstart < end; nstart = nend) {
 432                /*
 433                 * We want to fault in pages for [nstart; end) address range.
 434                 * Find first corresponding VMA.
 435                 */
 436                if (!locked) {
 437                        locked = 1;
 438                        down_read(&mm->mmap_sem);
 439                        vma = find_vma(mm, nstart);
 440                } else if (nstart >= vma->vm_end)
 441                        vma = vma->vm_next;
 442                if (!vma || vma->vm_start >= end)
 443                        break;
 444                /*
 445                 * Set [nstart; nend) to intersection of desired address
 446                 * range with the first VMA. Also, skip undesirable VMA types.
 447                 */
 448                nend = min(end, vma->vm_end);
 449                if (vma->vm_flags & (VM_IO | VM_PFNMAP))
 450                        continue;
 451                if (nstart < vma->vm_start)
 452                        nstart = vma->vm_start;
 453                /*
 454                 * Now fault in a range of pages. __mlock_vma_pages_range()
 455                 * double checks the vma flags, so that it won't mlock pages
 456                 * if the vma was already munlocked.
 457                 */
 458                ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
 459                if (ret < 0) {
 460                        if (ignore_errors) {
 461                                ret = 0;
 462                                continue;       /* continue at next VMA */
 463                        }
 464                        ret = __mlock_posix_error_return(ret);
 465                        break;
 466                }
 467                nend = nstart + ret * PAGE_SIZE;
 468                ret = 0;
 469        }
 470        if (locked)
 471                up_read(&mm->mmap_sem);
 472        return ret;     /* 0 or negative error code */
 473}
 474
 475SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 476{
 477        unsigned long locked;
 478        unsigned long lock_limit;
 479        int error = -ENOMEM;
 480
 481        if (!can_do_mlock())
 482                return -EPERM;
 483
 484        lru_add_drain_all();    /* flush pagevec */
 485
 486        down_write(&current->mm->mmap_sem);
 487        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 488        start &= PAGE_MASK;
 489
 490        locked = len >> PAGE_SHIFT;
 491        locked += current->mm->locked_vm;
 492
 493        lock_limit = rlimit(RLIMIT_MEMLOCK);
 494        lock_limit >>= PAGE_SHIFT;
 495
 496        /* check against resource limits */
 497        if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
 498                error = do_mlock(start, len, 1);
 499        up_write(&current->mm->mmap_sem);
 500        if (!error)
 501                error = do_mlock_pages(start, len, 0);
 502        return error;
 503}
 504
 505SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
 506{
 507        int ret;
 508
 509        down_write(&current->mm->mmap_sem);
 510        len = PAGE_ALIGN(len + (start & ~PAGE_MASK));
 511        start &= PAGE_MASK;
 512        ret = do_mlock(start, len, 0);
 513        up_write(&current->mm->mmap_sem);
 514        return ret;
 515}
 516
 517static int do_mlockall(int flags)
 518{
 519        struct vm_area_struct * vma, * prev = NULL;
 520        unsigned int def_flags = 0;
 521
 522        if (flags & MCL_FUTURE)
 523                def_flags = VM_LOCKED;
 524        current->mm->def_flags = def_flags;
 525        if (flags == MCL_FUTURE)
 526                goto out;
 527
 528        for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
 529                vm_flags_t newflags;
 530
 531                newflags = vma->vm_flags | VM_LOCKED;
 532                if (!(flags & MCL_CURRENT))
 533                        newflags &= ~VM_LOCKED;
 534
 535                /* Ignore errors */
 536                mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
 537        }
 538out:
 539        return 0;
 540}
 541
 542SYSCALL_DEFINE1(mlockall, int, flags)
 543{
 544        unsigned long lock_limit;
 545        int ret = -EINVAL;
 546
 547        if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE)))
 548                goto out;
 549
 550        ret = -EPERM;
 551        if (!can_do_mlock())
 552                goto out;
 553
 554        if (flags & MCL_CURRENT)
 555                lru_add_drain_all();    /* flush pagevec */
 556
 557        down_write(&current->mm->mmap_sem);
 558
 559        lock_limit = rlimit(RLIMIT_MEMLOCK);
 560        lock_limit >>= PAGE_SHIFT;
 561
 562        ret = -ENOMEM;
 563        if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
 564            capable(CAP_IPC_LOCK))
 565                ret = do_mlockall(flags);
 566        up_write(&current->mm->mmap_sem);
 567        if (!ret && (flags & MCL_CURRENT)) {
 568                /* Ignore errors */
 569                do_mlock_pages(0, TASK_SIZE, 1);
 570        }
 571out:
 572        return ret;
 573}
 574
 575SYSCALL_DEFINE0(munlockall)
 576{
 577        int ret;
 578
 579        down_write(&current->mm->mmap_sem);
 580        ret = do_mlockall(0);
 581        up_write(&current->mm->mmap_sem);
 582        return ret;
 583}
 584
 585/*
 586 * Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
 587 * shm segments) get accounted against the user_struct instead.
 588 */
 589static DEFINE_SPINLOCK(shmlock_user_lock);
 590
 591int user_shm_lock(size_t size, struct user_struct *user)
 592{
 593        unsigned long lock_limit, locked;
 594        int allowed = 0;
 595
 596        locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 597        lock_limit = rlimit(RLIMIT_MEMLOCK);
 598        if (lock_limit == RLIM_INFINITY)
 599                allowed = 1;
 600        lock_limit >>= PAGE_SHIFT;
 601        spin_lock(&shmlock_user_lock);
 602        if (!allowed &&
 603            locked + user->locked_shm > lock_limit && !capable(CAP_IPC_LOCK))
 604                goto out;
 605        get_uid(user);
 606        user->locked_shm += locked;
 607        allowed = 1;
 608out:
 609        spin_unlock(&shmlock_user_lock);
 610        return allowed;
 611}
 612
 613void user_shm_unlock(size_t size, struct user_struct *user)
 614{
 615        spin_lock(&shmlock_user_lock);
 616        user->locked_shm -= (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 617        spin_unlock(&shmlock_user_lock);
 618        free_uid(user);
 619}
 620
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