linux/mm/mremap.c
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   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/swapops.h>
  19#include <linux/highmem.h>
  20#include <linux/security.h>
  21#include <linux/syscalls.h>
  22#include <linux/mmu_notifier.h>
  23#include <linux/sched/sysctl.h>
  24
  25#include <asm/uaccess.h>
  26#include <asm/cacheflush.h>
  27#include <asm/tlbflush.h>
  28
  29#include "internal.h"
  30
  31static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
  32{
  33        pgd_t *pgd;
  34        pud_t *pud;
  35        pmd_t *pmd;
  36
  37        pgd = pgd_offset(mm, addr);
  38        if (pgd_none_or_clear_bad(pgd))
  39                return NULL;
  40
  41        pud = pud_offset(pgd, addr);
  42        if (pud_none_or_clear_bad(pud))
  43                return NULL;
  44
  45        pmd = pmd_offset(pud, addr);
  46        if (pmd_none(*pmd))
  47                return NULL;
  48
  49        return pmd;
  50}
  51
  52static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  53                            unsigned long addr)
  54{
  55        pgd_t *pgd;
  56        pud_t *pud;
  57        pmd_t *pmd;
  58
  59        pgd = pgd_offset(mm, addr);
  60        pud = pud_alloc(mm, pgd, addr);
  61        if (!pud)
  62                return NULL;
  63
  64        pmd = pmd_alloc(mm, pud, addr);
  65        if (!pmd)
  66                return NULL;
  67
  68        VM_BUG_ON(pmd_trans_huge(*pmd));
  69
  70        return pmd;
  71}
  72
  73static pte_t move_soft_dirty_pte(pte_t pte)
  74{
  75        /*
  76         * Set soft dirty bit so we can notice
  77         * in userspace the ptes were moved.
  78         */
  79#ifdef CONFIG_MEM_SOFT_DIRTY
  80        if (pte_present(pte))
  81                pte = pte_mksoft_dirty(pte);
  82        else if (is_swap_pte(pte))
  83                pte = pte_swp_mksoft_dirty(pte);
  84        else if (pte_file(pte))
  85                pte = pte_file_mksoft_dirty(pte);
  86#endif
  87        return pte;
  88}
  89
  90static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
  91                unsigned long old_addr, unsigned long old_end,
  92                struct vm_area_struct *new_vma, pmd_t *new_pmd,
  93                unsigned long new_addr, bool need_rmap_locks)
  94{
  95        struct address_space *mapping = NULL;
  96        struct anon_vma *anon_vma = NULL;
  97        struct mm_struct *mm = vma->vm_mm;
  98        pte_t *old_pte, *new_pte, pte;
  99        spinlock_t *old_ptl, *new_ptl;
 100
 101        /*
 102         * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
 103         * locks to ensure that rmap will always observe either the old or the
 104         * new ptes. This is the easiest way to avoid races with
 105         * truncate_pagecache(), page migration, etc...
 106         *
 107         * When need_rmap_locks is false, we use other ways to avoid
 108         * such races:
 109         *
 110         * - During exec() shift_arg_pages(), we use a specially tagged vma
 111         *   which rmap call sites look for using is_vma_temporary_stack().
 112         *
 113         * - During mremap(), new_vma is often known to be placed after vma
 114         *   in rmap traversal order. This ensures rmap will always observe
 115         *   either the old pte, or the new pte, or both (the page table locks
 116         *   serialize access to individual ptes, but only rmap traversal
 117         *   order guarantees that we won't miss both the old and new ptes).
 118         */
 119        if (need_rmap_locks) {
 120                if (vma->vm_file) {
 121                        mapping = vma->vm_file->f_mapping;
 122                        mutex_lock(&mapping->i_mmap_mutex);
 123                }
 124                if (vma->anon_vma) {
 125                        anon_vma = vma->anon_vma;
 126                        anon_vma_lock_write(anon_vma);
 127                }
 128        }
 129
 130        /*
 131         * We don't have to worry about the ordering of src and dst
 132         * pte locks because exclusive mmap_sem prevents deadlock.
 133         */
 134        old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 135        new_pte = pte_offset_map(new_pmd, new_addr);
 136        new_ptl = pte_lockptr(mm, new_pmd);
 137        if (new_ptl != old_ptl)
 138                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 139        arch_enter_lazy_mmu_mode();
 140
 141        for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 142                                   new_pte++, new_addr += PAGE_SIZE) {
 143                if (pte_none(*old_pte))
 144                        continue;
 145                pte = ptep_get_and_clear(mm, old_addr, old_pte);
 146                pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
 147                pte = move_soft_dirty_pte(pte);
 148                set_pte_at(mm, new_addr, new_pte, pte);
 149        }
 150
 151        arch_leave_lazy_mmu_mode();
 152        if (new_ptl != old_ptl)
 153                spin_unlock(new_ptl);
 154        pte_unmap(new_pte - 1);
 155        pte_unmap_unlock(old_pte - 1, old_ptl);
 156        if (anon_vma)
 157                anon_vma_unlock_write(anon_vma);
 158        if (mapping)
 159                mutex_unlock(&mapping->i_mmap_mutex);
 160}
 161
 162#define LATENCY_LIMIT   (64 * PAGE_SIZE)
 163
 164unsigned long move_page_tables(struct vm_area_struct *vma,
 165                unsigned long old_addr, struct vm_area_struct *new_vma,
 166                unsigned long new_addr, unsigned long len,
 167                bool need_rmap_locks)
 168{
 169        unsigned long extent, next, old_end;
 170        pmd_t *old_pmd, *new_pmd;
 171        bool need_flush = false;
 172        unsigned long mmun_start;       /* For mmu_notifiers */
 173        unsigned long mmun_end;         /* For mmu_notifiers */
 174
 175        old_end = old_addr + len;
 176        flush_cache_range(vma, old_addr, old_end);
 177
 178        mmun_start = old_addr;
 179        mmun_end   = old_end;
 180        mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
 181
 182        for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 183                cond_resched();
 184                next = (old_addr + PMD_SIZE) & PMD_MASK;
 185                /* even if next overflowed, extent below will be ok */
 186                extent = next - old_addr;
 187                if (extent > old_end - old_addr)
 188                        extent = old_end - old_addr;
 189                old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 190                if (!old_pmd)
 191                        continue;
 192                new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 193                if (!new_pmd)
 194                        break;
 195                if (pmd_trans_huge(*old_pmd)) {
 196                        int err = 0;
 197                        if (extent == HPAGE_PMD_SIZE)
 198                                err = move_huge_pmd(vma, new_vma, old_addr,
 199                                                    new_addr, old_end,
 200                                                    old_pmd, new_pmd);
 201                        if (err > 0) {
 202                                need_flush = true;
 203                                continue;
 204                        } else if (!err) {
 205                                split_huge_page_pmd(vma, old_addr, old_pmd);
 206                        }
 207                        VM_BUG_ON(pmd_trans_huge(*old_pmd));
 208                }
 209                if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
 210                                                      new_pmd, new_addr))
 211                        break;
 212                next = (new_addr + PMD_SIZE) & PMD_MASK;
 213                if (extent > next - new_addr)
 214                        extent = next - new_addr;
 215                if (extent > LATENCY_LIMIT)
 216                        extent = LATENCY_LIMIT;
 217                move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 218                          new_vma, new_pmd, new_addr, need_rmap_locks);
 219                need_flush = true;
 220        }
 221        if (likely(need_flush))
 222                flush_tlb_range(vma, old_end-len, old_addr);
 223
 224        mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
 225
 226        return len + old_addr - old_end;        /* how much done */
 227}
 228
 229static unsigned long move_vma(struct vm_area_struct *vma,
 230                unsigned long old_addr, unsigned long old_len,
 231                unsigned long new_len, unsigned long new_addr, bool *locked)
 232{
 233        struct mm_struct *mm = vma->vm_mm;
 234        struct vm_area_struct *new_vma;
 235        unsigned long vm_flags = vma->vm_flags;
 236        unsigned long new_pgoff;
 237        unsigned long moved_len;
 238        unsigned long excess = 0;
 239        unsigned long hiwater_vm;
 240        int split = 0;
 241        int err;
 242        bool need_rmap_locks;
 243
 244        /*
 245         * We'd prefer to avoid failure later on in do_munmap:
 246         * which may split one vma into three before unmapping.
 247         */
 248        if (mm->map_count >= sysctl_max_map_count - 3)
 249                return -ENOMEM;
 250
 251        /*
 252         * Advise KSM to break any KSM pages in the area to be moved:
 253         * it would be confusing if they were to turn up at the new
 254         * location, where they happen to coincide with different KSM
 255         * pages recently unmapped.  But leave vma->vm_flags as it was,
 256         * so KSM can come around to merge on vma and new_vma afterwards.
 257         */
 258        err = ksm_madvise(vma, old_addr, old_addr + old_len,
 259                                                MADV_UNMERGEABLE, &vm_flags);
 260        if (err)
 261                return err;
 262
 263        new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 264        new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 265                           &need_rmap_locks);
 266        if (!new_vma)
 267                return -ENOMEM;
 268
 269        moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 270                                     need_rmap_locks);
 271        if (moved_len < old_len) {
 272                /*
 273                 * On error, move entries back from new area to old,
 274                 * which will succeed since page tables still there,
 275                 * and then proceed to unmap new area instead of old.
 276                 */
 277                move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 278                                 true);
 279                vma = new_vma;
 280                old_len = new_len;
 281                old_addr = new_addr;
 282                new_addr = -ENOMEM;
 283        }
 284
 285        /* Conceal VM_ACCOUNT so old reservation is not undone */
 286        if (vm_flags & VM_ACCOUNT) {
 287                vma->vm_flags &= ~VM_ACCOUNT;
 288                excess = vma->vm_end - vma->vm_start - old_len;
 289                if (old_addr > vma->vm_start &&
 290                    old_addr + old_len < vma->vm_end)
 291                        split = 1;
 292        }
 293
 294        /*
 295         * If we failed to move page tables we still do total_vm increment
 296         * since do_munmap() will decrement it by old_len == new_len.
 297         *
 298         * Since total_vm is about to be raised artificially high for a
 299         * moment, we need to restore high watermark afterwards: if stats
 300         * are taken meanwhile, total_vm and hiwater_vm appear too high.
 301         * If this were a serious issue, we'd add a flag to do_munmap().
 302         */
 303        hiwater_vm = mm->hiwater_vm;
 304        vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
 305
 306        if (do_munmap(mm, old_addr, old_len) < 0) {
 307                /* OOM: unable to split vma, just get accounts right */
 308                vm_unacct_memory(excess >> PAGE_SHIFT);
 309                excess = 0;
 310        }
 311        mm->hiwater_vm = hiwater_vm;
 312
 313        /* Restore VM_ACCOUNT if one or two pieces of vma left */
 314        if (excess) {
 315                vma->vm_flags |= VM_ACCOUNT;
 316                if (split)
 317                        vma->vm_next->vm_flags |= VM_ACCOUNT;
 318        }
 319
 320        if (vm_flags & VM_LOCKED) {
 321                mm->locked_vm += new_len >> PAGE_SHIFT;
 322                *locked = true;
 323        }
 324
 325        return new_addr;
 326}
 327
 328static struct vm_area_struct *vma_to_resize(unsigned long addr,
 329        unsigned long old_len, unsigned long new_len, unsigned long *p)
 330{
 331        struct mm_struct *mm = current->mm;
 332        struct vm_area_struct *vma = find_vma(mm, addr);
 333
 334        if (!vma || vma->vm_start > addr)
 335                goto Efault;
 336
 337        if (is_vm_hugetlb_page(vma))
 338                goto Einval;
 339
 340        /* We can't remap across vm area boundaries */
 341        if (old_len > vma->vm_end - addr)
 342                goto Efault;
 343
 344        /* Need to be careful about a growing mapping */
 345        if (new_len > old_len) {
 346                unsigned long pgoff;
 347
 348                if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 349                        goto Efault;
 350                pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 351                pgoff += vma->vm_pgoff;
 352                if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 353                        goto Einval;
 354        }
 355
 356        if (vma->vm_flags & VM_LOCKED) {
 357                unsigned long locked, lock_limit;
 358                locked = mm->locked_vm << PAGE_SHIFT;
 359                lock_limit = rlimit(RLIMIT_MEMLOCK);
 360                locked += new_len - old_len;
 361                if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 362                        goto Eagain;
 363        }
 364
 365        if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
 366                goto Enomem;
 367
 368        if (vma->vm_flags & VM_ACCOUNT) {
 369                unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 370                if (security_vm_enough_memory_mm(mm, charged))
 371                        goto Efault;
 372                *p = charged;
 373        }
 374
 375        return vma;
 376
 377Efault: /* very odd choice for most of the cases, but... */
 378        return ERR_PTR(-EFAULT);
 379Einval:
 380        return ERR_PTR(-EINVAL);
 381Enomem:
 382        return ERR_PTR(-ENOMEM);
 383Eagain:
 384        return ERR_PTR(-EAGAIN);
 385}
 386
 387static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 388                unsigned long new_addr, unsigned long new_len, bool *locked)
 389{
 390        struct mm_struct *mm = current->mm;
 391        struct vm_area_struct *vma;
 392        unsigned long ret = -EINVAL;
 393        unsigned long charged = 0;
 394        unsigned long map_flags;
 395
 396        if (new_addr & ~PAGE_MASK)
 397                goto out;
 398
 399        if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 400                goto out;
 401
 402        /* Check if the location we're moving into overlaps the
 403         * old location at all, and fail if it does.
 404         */
 405        if ((new_addr <= addr) && (new_addr+new_len) > addr)
 406                goto out;
 407
 408        if ((addr <= new_addr) && (addr+old_len) > new_addr)
 409                goto out;
 410
 411        ret = do_munmap(mm, new_addr, new_len);
 412        if (ret)
 413                goto out;
 414
 415        if (old_len >= new_len) {
 416                ret = do_munmap(mm, addr+new_len, old_len - new_len);
 417                if (ret && old_len != new_len)
 418                        goto out;
 419                old_len = new_len;
 420        }
 421
 422        vma = vma_to_resize(addr, old_len, new_len, &charged);
 423        if (IS_ERR(vma)) {
 424                ret = PTR_ERR(vma);
 425                goto out;
 426        }
 427
 428        map_flags = MAP_FIXED;
 429        if (vma->vm_flags & VM_MAYSHARE)
 430                map_flags |= MAP_SHARED;
 431
 432        ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 433                                ((addr - vma->vm_start) >> PAGE_SHIFT),
 434                                map_flags);
 435        if (ret & ~PAGE_MASK)
 436                goto out1;
 437
 438        ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
 439        if (!(ret & ~PAGE_MASK))
 440                goto out;
 441out1:
 442        vm_unacct_memory(charged);
 443
 444out:
 445        return ret;
 446}
 447
 448static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 449{
 450        unsigned long end = vma->vm_end + delta;
 451        if (end < vma->vm_end) /* overflow */
 452                return 0;
 453        if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 454                return 0;
 455        if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 456                              0, MAP_FIXED) & ~PAGE_MASK)
 457                return 0;
 458        return 1;
 459}
 460
 461/*
 462 * Expand (or shrink) an existing mapping, potentially moving it at the
 463 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 464 *
 465 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 466 * This option implies MREMAP_MAYMOVE.
 467 */
 468SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 469                unsigned long, new_len, unsigned long, flags,
 470                unsigned long, new_addr)
 471{
 472        struct mm_struct *mm = current->mm;
 473        struct vm_area_struct *vma;
 474        unsigned long ret = -EINVAL;
 475        unsigned long charged = 0;
 476        bool locked = false;
 477
 478        if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 479                return ret;
 480
 481        if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 482                return ret;
 483
 484        if (addr & ~PAGE_MASK)
 485                return ret;
 486
 487        old_len = PAGE_ALIGN(old_len);
 488        new_len = PAGE_ALIGN(new_len);
 489
 490        /*
 491         * We allow a zero old-len as a special case
 492         * for DOS-emu "duplicate shm area" thing. But
 493         * a zero new-len is nonsensical.
 494         */
 495        if (!new_len)
 496                return ret;
 497
 498        down_write(&current->mm->mmap_sem);
 499
 500        if (flags & MREMAP_FIXED) {
 501                ret = mremap_to(addr, old_len, new_addr, new_len,
 502                                &locked);
 503                goto out;
 504        }
 505
 506        /*
 507         * Always allow a shrinking remap: that just unmaps
 508         * the unnecessary pages..
 509         * do_munmap does all the needed commit accounting
 510         */
 511        if (old_len >= new_len) {
 512                ret = do_munmap(mm, addr+new_len, old_len - new_len);
 513                if (ret && old_len != new_len)
 514                        goto out;
 515                ret = addr;
 516                goto out;
 517        }
 518
 519        /*
 520         * Ok, we need to grow..
 521         */
 522        vma = vma_to_resize(addr, old_len, new_len, &charged);
 523        if (IS_ERR(vma)) {
 524                ret = PTR_ERR(vma);
 525                goto out;
 526        }
 527
 528        /* old_len exactly to the end of the area..
 529         */
 530        if (old_len == vma->vm_end - addr) {
 531                /* can we just expand the current mapping? */
 532                if (vma_expandable(vma, new_len - old_len)) {
 533                        int pages = (new_len - old_len) >> PAGE_SHIFT;
 534
 535                        if (vma_adjust(vma, vma->vm_start, addr + new_len,
 536                                       vma->vm_pgoff, NULL)) {
 537                                ret = -ENOMEM;
 538                                goto out;
 539                        }
 540
 541                        vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
 542                        if (vma->vm_flags & VM_LOCKED) {
 543                                mm->locked_vm += pages;
 544                                locked = true;
 545                                new_addr = addr;
 546                        }
 547                        ret = addr;
 548                        goto out;
 549                }
 550        }
 551
 552        /*
 553         * We weren't able to just expand or shrink the area,
 554         * we need to create a new one and move it..
 555         */
 556        ret = -ENOMEM;
 557        if (flags & MREMAP_MAYMOVE) {
 558                unsigned long map_flags = 0;
 559                if (vma->vm_flags & VM_MAYSHARE)
 560                        map_flags |= MAP_SHARED;
 561
 562                new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 563                                        vma->vm_pgoff +
 564                                        ((addr - vma->vm_start) >> PAGE_SHIFT),
 565                                        map_flags);
 566                if (new_addr & ~PAGE_MASK) {
 567                        ret = new_addr;
 568                        goto out;
 569                }
 570
 571                ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
 572        }
 573out:
 574        if (ret & ~PAGE_MASK)
 575                vm_unacct_memory(charged);
 576        up_write(&current->mm->mmap_sem);
 577        if (locked && new_len > old_len)
 578                mm_populate(new_addr + old_len, new_len - old_len);
 579        return ret;
 580}
 581
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