linux/mm/mremap.c
<<
>>
Prefs
   1/*
   2 *      mm/mremap.c
   3 *
   4 *      (C) Copyright 1996 Linus Torvalds
   5 *
   6 *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
   7 *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
   8 */
   9
  10#include <linux/mm.h>
  11#include <linux/hugetlb.h>
  12#include <linux/shm.h>
  13#include <linux/ksm.h>
  14#include <linux/mman.h>
  15#include <linux/swap.h>
  16#include <linux/capability.h>
  17#include <linux/fs.h>
  18#include <linux/highmem.h>
  19#include <linux/security.h>
  20#include <linux/syscalls.h>
  21#include <linux/mmu_notifier.h>
  22#include <linux/sched/sysctl.h>
  23
  24#include <asm/uaccess.h>
  25#include <asm/cacheflush.h>
  26#include <asm/tlbflush.h>
  27
  28#include "internal.h"
  29
  30static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
  31{
  32        pgd_t *pgd;
  33        pud_t *pud;
  34        pmd_t *pmd;
  35
  36        pgd = pgd_offset(mm, addr);
  37        if (pgd_none_or_clear_bad(pgd))
  38                return NULL;
  39
  40        pud = pud_offset(pgd, addr);
  41        if (pud_none_or_clear_bad(pud))
  42                return NULL;
  43
  44        pmd = pmd_offset(pud, addr);
  45        if (pmd_none(*pmd))
  46                return NULL;
  47
  48        return pmd;
  49}
  50
  51static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  52                            unsigned long addr)
  53{
  54        pgd_t *pgd;
  55        pud_t *pud;
  56        pmd_t *pmd;
  57
  58        pgd = pgd_offset(mm, addr);
  59        pud = pud_alloc(mm, pgd, addr);
  60        if (!pud)
  61                return NULL;
  62
  63        pmd = pmd_alloc(mm, pud, addr);
  64        if (!pmd)
  65                return NULL;
  66
  67        VM_BUG_ON(pmd_trans_huge(*pmd));
  68
  69        return pmd;
  70}
  71
  72static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
  73                unsigned long old_addr, unsigned long old_end,
  74                struct vm_area_struct *new_vma, pmd_t *new_pmd,
  75                unsigned long new_addr, bool need_rmap_locks)
  76{
  77        struct address_space *mapping = NULL;
  78        struct anon_vma *anon_vma = NULL;
  79        struct mm_struct *mm = vma->vm_mm;
  80        pte_t *old_pte, *new_pte, pte;
  81        spinlock_t *old_ptl, *new_ptl;
  82
  83        /*
  84         * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
  85         * locks to ensure that rmap will always observe either the old or the
  86         * new ptes. This is the easiest way to avoid races with
  87         * truncate_pagecache(), page migration, etc...
  88         *
  89         * When need_rmap_locks is false, we use other ways to avoid
  90         * such races:
  91         *
  92         * - During exec() shift_arg_pages(), we use a specially tagged vma
  93         *   which rmap call sites look for using is_vma_temporary_stack().
  94         *
  95         * - During mremap(), new_vma is often known to be placed after vma
  96         *   in rmap traversal order. This ensures rmap will always observe
  97         *   either the old pte, or the new pte, or both (the page table locks
  98         *   serialize access to individual ptes, but only rmap traversal
  99         *   order guarantees that we won't miss both the old and new ptes).
 100         */
 101        if (need_rmap_locks) {
 102                if (vma->vm_file) {
 103                        mapping = vma->vm_file->f_mapping;
 104                        mutex_lock(&mapping->i_mmap_mutex);
 105                }
 106                if (vma->anon_vma) {
 107                        anon_vma = vma->anon_vma;
 108                        anon_vma_lock_write(anon_vma);
 109                }
 110        }
 111
 112        /*
 113         * We don't have to worry about the ordering of src and dst
 114         * pte locks because exclusive mmap_sem prevents deadlock.
 115         */
 116        old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 117        new_pte = pte_offset_map(new_pmd, new_addr);
 118        new_ptl = pte_lockptr(mm, new_pmd);
 119        if (new_ptl != old_ptl)
 120                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 121        arch_enter_lazy_mmu_mode();
 122
 123        for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 124                                   new_pte++, new_addr += PAGE_SIZE) {
 125                if (pte_none(*old_pte))
 126                        continue;
 127                pte = ptep_get_and_clear(mm, old_addr, old_pte);
 128                pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
 129                set_pte_at(mm, new_addr, new_pte, pte);
 130        }
 131
 132        arch_leave_lazy_mmu_mode();
 133        if (new_ptl != old_ptl)
 134                spin_unlock(new_ptl);
 135        pte_unmap(new_pte - 1);
 136        pte_unmap_unlock(old_pte - 1, old_ptl);
 137        if (anon_vma)
 138                anon_vma_unlock_write(anon_vma);
 139        if (mapping)
 140                mutex_unlock(&mapping->i_mmap_mutex);
 141}
 142
 143#define LATENCY_LIMIT   (64 * PAGE_SIZE)
 144
 145unsigned long move_page_tables(struct vm_area_struct *vma,
 146                unsigned long old_addr, struct vm_area_struct *new_vma,
 147                unsigned long new_addr, unsigned long len,
 148                bool need_rmap_locks)
 149{
 150        unsigned long extent, next, old_end;
 151        pmd_t *old_pmd, *new_pmd;
 152        bool need_flush = false;
 153        unsigned long mmun_start;       /* For mmu_notifiers */
 154        unsigned long mmun_end;         /* For mmu_notifiers */
 155
 156        old_end = old_addr + len;
 157        flush_cache_range(vma, old_addr, old_end);
 158
 159        mmun_start = old_addr;
 160        mmun_end   = old_end;
 161        mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 162
 163        for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 164                cond_resched();
 165                next = (old_addr + PMD_SIZE) & PMD_MASK;
 166                /* even if next overflowed, extent below will be ok */
 167                extent = next - old_addr;
 168                if (extent > old_end - old_addr)
 169                        extent = old_end - old_addr;
 170                old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 171                if (!old_pmd)
 172                        continue;
 173                new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 174                if (!new_pmd)
 175                        break;
 176                if (pmd_trans_huge(*old_pmd)) {
 177                        int err = 0;
 178                        if (extent == HPAGE_PMD_SIZE)
 179                                err = move_huge_pmd(vma, new_vma, old_addr,
 180                                                    new_addr, old_end,
 181                                                    old_pmd, new_pmd);
 182                        if (err > 0) {
 183                                need_flush = true;
 184                                continue;
 185                        } else if (!err) {
 186                                split_huge_page_pmd(vma, old_addr, old_pmd);
 187                        }
 188                        VM_BUG_ON(pmd_trans_huge(*old_pmd));
 189                }
 190                if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
 191                                                      new_pmd, new_addr))
 192                        break;
 193                next = (new_addr + PMD_SIZE) & PMD_MASK;
 194                if (extent > next - new_addr)
 195                        extent = next - new_addr;
 196                if (extent > LATENCY_LIMIT)
 197                        extent = LATENCY_LIMIT;
 198                move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 199                          new_vma, new_pmd, new_addr, need_rmap_locks);
 200                need_flush = true;
 201        }
 202        if (likely(need_flush))
 203                flush_tlb_range(vma, old_end-len, old_addr);
 204
 205        mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 206
 207        return len + old_addr - old_end;        /* how much done */
 208}
 209
 210static unsigned long move_vma(struct vm_area_struct *vma,
 211                unsigned long old_addr, unsigned long old_len,
 212                unsigned long new_len, unsigned long new_addr, bool *locked)
 213{
 214        struct mm_struct *mm = vma->vm_mm;
 215        struct vm_area_struct *new_vma;
 216        unsigned long vm_flags = vma->vm_flags;
 217        unsigned long new_pgoff;
 218        unsigned long moved_len;
 219        unsigned long excess = 0;
 220        unsigned long hiwater_vm;
 221        int split = 0;
 222        int err;
 223        bool need_rmap_locks;
 224
 225        /*
 226         * We'd prefer to avoid failure later on in do_munmap:
 227         * which may split one vma into three before unmapping.
 228         */
 229        if (mm->map_count >= sysctl_max_map_count - 3)
 230                return -ENOMEM;
 231
 232        /*
 233         * Advise KSM to break any KSM pages in the area to be moved:
 234         * it would be confusing if they were to turn up at the new
 235         * location, where they happen to coincide with different KSM
 236         * pages recently unmapped.  But leave vma->vm_flags as it was,
 237         * so KSM can come around to merge on vma and new_vma afterwards.
 238         */
 239        err = ksm_madvise(vma, old_addr, old_addr + old_len,
 240                                                MADV_UNMERGEABLE, &vm_flags);
 241        if (err)
 242                return err;
 243
 244        new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 245        new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 246                           &need_rmap_locks);
 247        if (!new_vma)
 248                return -ENOMEM;
 249
 250        moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 251                                     need_rmap_locks);
 252        if (moved_len < old_len) {
 253                /*
 254                 * On error, move entries back from new area to old,
 255                 * which will succeed since page tables still there,
 256                 * and then proceed to unmap new area instead of old.
 257                 */
 258                move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 259                                 true);
 260                vma = new_vma;
 261                old_len = new_len;
 262                old_addr = new_addr;
 263                new_addr = -ENOMEM;
 264        }
 265
 266        /* Conceal VM_ACCOUNT so old reservation is not undone */
 267        if (vm_flags & VM_ACCOUNT) {
 268                vma->vm_flags &= ~VM_ACCOUNT;
 269                excess = vma->vm_end - vma->vm_start - old_len;
 270                if (old_addr > vma->vm_start &&
 271                    old_addr + old_len < vma->vm_end)
 272                        split = 1;
 273        }
 274
 275        /*
 276         * If we failed to move page tables we still do total_vm increment
 277         * since do_munmap() will decrement it by old_len == new_len.
 278         *
 279         * Since total_vm is about to be raised artificially high for a
 280         * moment, we need to restore high watermark afterwards: if stats
 281         * are taken meanwhile, total_vm and hiwater_vm appear too high.
 282         * If this were a serious issue, we'd add a flag to do_munmap().
 283         */
 284        hiwater_vm = mm->hiwater_vm;
 285        vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
 286
 287        if (do_munmap(mm, old_addr, old_len) < 0) {
 288                /* OOM: unable to split vma, just get accounts right */
 289                vm_unacct_memory(excess >> PAGE_SHIFT);
 290                excess = 0;
 291        }
 292        mm->hiwater_vm = hiwater_vm;
 293
 294        /* Restore VM_ACCOUNT if one or two pieces of vma left */
 295        if (excess) {
 296                vma->vm_flags |= VM_ACCOUNT;
 297                if (split)
 298                        vma->vm_next->vm_flags |= VM_ACCOUNT;
 299        }
 300
 301        if (vm_flags & VM_LOCKED) {
 302                mm->locked_vm += new_len >> PAGE_SHIFT;
 303                *locked = true;
 304        }
 305
 306        return new_addr;
 307}
 308
 309static struct vm_area_struct *vma_to_resize(unsigned long addr,
 310        unsigned long old_len, unsigned long new_len, unsigned long *p)
 311{
 312        struct mm_struct *mm = current->mm;
 313        struct vm_area_struct *vma = find_vma(mm, addr);
 314
 315        if (!vma || vma->vm_start > addr)
 316                goto Efault;
 317
 318        if (is_vm_hugetlb_page(vma))
 319                goto Einval;
 320
 321        /* We can't remap across vm area boundaries */
 322        if (old_len > vma->vm_end - addr)
 323                goto Efault;
 324
 325        /* Need to be careful about a growing mapping */
 326        if (new_len > old_len) {
 327                unsigned long pgoff;
 328
 329                if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 330                        goto Efault;
 331                pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 332                pgoff += vma->vm_pgoff;
 333                if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 334                        goto Einval;
 335        }
 336
 337        if (vma->vm_flags & VM_LOCKED) {
 338                unsigned long locked, lock_limit;
 339                locked = mm->locked_vm << PAGE_SHIFT;
 340                lock_limit = rlimit(RLIMIT_MEMLOCK);
 341                locked += new_len - old_len;
 342                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 343                        goto Eagain;
 344        }
 345
 346        if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
 347                goto Enomem;
 348
 349        if (vma->vm_flags & VM_ACCOUNT) {
 350                unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 351                if (security_vm_enough_memory_mm(mm, charged))
 352                        goto Efault;
 353                *p = charged;
 354        }
 355
 356        return vma;
 357
 358Efault: /* very odd choice for most of the cases, but... */
 359        return ERR_PTR(-EFAULT);
 360Einval:
 361        return ERR_PTR(-EINVAL);
 362Enomem:
 363        return ERR_PTR(-ENOMEM);
 364Eagain:
 365        return ERR_PTR(-EAGAIN);
 366}
 367
 368static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 369                unsigned long new_addr, unsigned long new_len, bool *locked)
 370{
 371        struct mm_struct *mm = current->mm;
 372        struct vm_area_struct *vma;
 373        unsigned long ret = -EINVAL;
 374        unsigned long charged = 0;
 375        unsigned long map_flags;
 376
 377        if (new_addr & ~PAGE_MASK)
 378                goto out;
 379
 380        if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 381                goto out;
 382
 383        /* Check if the location we're moving into overlaps the
 384         * old location at all, and fail if it does.
 385         */
 386        if ((new_addr <= addr) && (new_addr+new_len) > addr)
 387                goto out;
 388
 389        if ((addr <= new_addr) && (addr+old_len) > new_addr)
 390                goto out;
 391
 392        ret = do_munmap(mm, new_addr, new_len);
 393        if (ret)
 394                goto out;
 395
 396        if (old_len >= new_len) {
 397                ret = do_munmap(mm, addr+new_len, old_len - new_len);
 398                if (ret && old_len != new_len)
 399                        goto out;
 400                old_len = new_len;
 401        }
 402
 403        vma = vma_to_resize(addr, old_len, new_len, &charged);
 404        if (IS_ERR(vma)) {
 405                ret = PTR_ERR(vma);
 406                goto out;
 407        }
 408
 409        map_flags = MAP_FIXED;
 410        if (vma->vm_flags & VM_MAYSHARE)
 411                map_flags |= MAP_SHARED;
 412
 413        ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 414                                ((addr - vma->vm_start) >> PAGE_SHIFT),
 415                                map_flags);
 416        if (ret & ~PAGE_MASK)
 417                goto out1;
 418
 419        ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
 420        if (!(ret & ~PAGE_MASK))
 421                goto out;
 422out1:
 423        vm_unacct_memory(charged);
 424
 425out:
 426        return ret;
 427}
 428
 429static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 430{
 431        unsigned long end = vma->vm_end + delta;
 432        if (end < vma->vm_end) /* overflow */
 433                return 0;
 434        if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 435                return 0;
 436        if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 437                              0, MAP_FIXED) & ~PAGE_MASK)
 438                return 0;
 439        return 1;
 440}
 441
 442/*
 443 * Expand (or shrink) an existing mapping, potentially moving it at the
 444 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 445 *
 446 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 447 * This option implies MREMAP_MAYMOVE.
 448 */
 449SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 450                unsigned long, new_len, unsigned long, flags,
 451                unsigned long, new_addr)
 452{
 453        struct mm_struct *mm = current->mm;
 454        struct vm_area_struct *vma;
 455        unsigned long ret = -EINVAL;
 456        unsigned long charged = 0;
 457        bool locked = false;
 458
 459        down_write(&current->mm->mmap_sem);
 460
 461        if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 462                goto out;
 463
 464        if (addr & ~PAGE_MASK)
 465                goto out;
 466
 467        old_len = PAGE_ALIGN(old_len);
 468        new_len = PAGE_ALIGN(new_len);
 469
 470        /*
 471         * We allow a zero old-len as a special case
 472         * for DOS-emu "duplicate shm area" thing. But
 473         * a zero new-len is nonsensical.
 474         */
 475        if (!new_len)
 476                goto out;
 477
 478        if (flags & MREMAP_FIXED) {
 479                if (flags & MREMAP_MAYMOVE)
 480                        ret = mremap_to(addr, old_len, new_addr, new_len,
 481                                        &locked);
 482                goto out;
 483        }
 484
 485        /*
 486         * Always allow a shrinking remap: that just unmaps
 487         * the unnecessary pages..
 488         * do_munmap does all the needed commit accounting
 489         */
 490        if (old_len >= new_len) {
 491                ret = do_munmap(mm, addr+new_len, old_len - new_len);
 492                if (ret && old_len != new_len)
 493                        goto out;
 494                ret = addr;
 495                goto out;
 496        }
 497
 498        /*
 499         * Ok, we need to grow..
 500         */
 501        vma = vma_to_resize(addr, old_len, new_len, &charged);
 502        if (IS_ERR(vma)) {
 503                ret = PTR_ERR(vma);
 504                goto out;
 505        }
 506
 507        /* old_len exactly to the end of the area..
 508         */
 509        if (old_len == vma->vm_end - addr) {
 510                /* can we just expand the current mapping? */
 511                if (vma_expandable(vma, new_len - old_len)) {
 512                        int pages = (new_len - old_len) >> PAGE_SHIFT;
 513
 514                        if (vma_adjust(vma, vma->vm_start, addr + new_len,
 515                                       vma->vm_pgoff, NULL)) {
 516                                ret = -ENOMEM;
 517                                goto out;
 518                        }
 519
 520                        vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
 521                        if (vma->vm_flags & VM_LOCKED) {
 522                                mm->locked_vm += pages;
 523                                locked = true;
 524                                new_addr = addr;
 525                        }
 526                        ret = addr;
 527                        goto out;
 528                }
 529        }
 530
 531        /*
 532         * We weren't able to just expand or shrink the area,
 533         * we need to create a new one and move it..
 534         */
 535        ret = -ENOMEM;
 536        if (flags & MREMAP_MAYMOVE) {
 537                unsigned long map_flags = 0;
 538                if (vma->vm_flags & VM_MAYSHARE)
 539                        map_flags |= MAP_SHARED;
 540
 541                new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 542                                        vma->vm_pgoff +
 543                                        ((addr - vma->vm_start) >> PAGE_SHIFT),
 544                                        map_flags);
 545                if (new_addr & ~PAGE_MASK) {
 546                        ret = new_addr;
 547                        goto out;
 548                }
 549
 550                ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
 551        }
 552out:
 553        if (ret & ~PAGE_MASK)
 554                vm_unacct_memory(charged);
 555        up_write(&current->mm->mmap_sem);
 556        if (locked && new_len > old_len)
 557                mm_populate(new_addr + old_len, new_len - old_len);
 558        return ret;
 559}
 560
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.