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