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