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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/uaccess.h>
24 #include <linux/mm-arch-hooks.h>
25
26 #include <asm/cacheflush.h>
27 #include <asm/tlbflush.h>
28
29 #include "internal.h"
30
31 static 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
52 static 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
73 static void take_rmap_locks(struct vm_area_struct *vma)
74 {
75 if (vma->vm_file)
76 i_mmap_lock_write(vma->vm_file->f_mapping);
77 if (vma->anon_vma)
78 anon_vma_lock_write(vma->anon_vma);
79 }
80
81 static void drop_rmap_locks(struct vm_area_struct *vma)
82 {
83 if (vma->anon_vma)
84 anon_vma_unlock_write(vma->anon_vma);
85 if (vma->vm_file)
86 i_mmap_unlock_write(vma->vm_file->f_mapping);
87 }
88
89 static pte_t move_soft_dirty_pte(pte_t pte)
90 {
91 /*
92 * Set soft dirty bit so we can notice
93 * in userspace the ptes were moved.
94 */
95 #ifdef CONFIG_MEM_SOFT_DIRTY
96 if (pte_present(pte))
97 pte = pte_mksoft_dirty(pte);
98 else if (is_swap_pte(pte))
99 pte = pte_swp_mksoft_dirty(pte);
100 #endif
101 return pte;
102 }
103
104 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
105 unsigned long old_addr, unsigned long old_end,
106 struct vm_area_struct *new_vma, pmd_t *new_pmd,
107 unsigned long new_addr, bool need_rmap_locks, bool *need_flush)
108 {
109 struct mm_struct *mm = vma->vm_mm;
110 pte_t *old_pte, *new_pte, pte;
111 spinlock_t *old_ptl, *new_ptl;
112 bool force_flush = false;
113 unsigned long len = old_end - old_addr;
114
115 /*
116 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
117 * locks to ensure that rmap will always observe either the old or the
118 * new ptes. This is the easiest way to avoid races with
119 * truncate_pagecache(), page migration, etc...
120 *
121 * When need_rmap_locks is false, we use other ways to avoid
122 * such races:
123 *
124 * - During exec() shift_arg_pages(), we use a specially tagged vma
125 * which rmap call sites look for using is_vma_temporary_stack().
126 *
127 * - During mremap(), new_vma is often known to be placed after vma
128 * in rmap traversal order. This ensures rmap will always observe
129 * either the old pte, or the new pte, or both (the page table locks
130 * serialize access to individual ptes, but only rmap traversal
131 * order guarantees that we won't miss both the old and new ptes).
132 */
133 if (need_rmap_locks)
134 take_rmap_locks(vma);
135
136 /*
137 * We don't have to worry about the ordering of src and dst
138 * pte locks because exclusive mmap_sem prevents deadlock.
139 */
140 old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
141 new_pte = pte_offset_map(new_pmd, new_addr);
142 new_ptl = pte_lockptr(mm, new_pmd);
143 if (new_ptl != old_ptl)
144 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
145 arch_enter_lazy_mmu_mode();
146
147 for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
148 new_pte++, new_addr += PAGE_SIZE) {
149 if (pte_none(*old_pte))
150 continue;
151
152 pte = ptep_get_and_clear(mm, old_addr, old_pte);
153 /*
154 * If we are remapping a dirty PTE, make sure
155 * to flush TLB before we drop the PTL for the
156 * old PTE or we may race with page_mkclean().
157 *
158 * This check has to be done after we removed the
159 * old PTE from page tables or another thread may
160 * dirty it after the check and before the removal.
161 */
162 if (pte_present(pte) && pte_dirty(pte))
163 force_flush = true;
164 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
165 pte = move_soft_dirty_pte(pte);
166 set_pte_at(mm, new_addr, new_pte, pte);
167 }
168
169 arch_leave_lazy_mmu_mode();
170 if (new_ptl != old_ptl)
171 spin_unlock(new_ptl);
172 pte_unmap(new_pte - 1);
173 if (force_flush)
174 flush_tlb_range(vma, old_end - len, old_end);
175 else
176 *need_flush = true;
177 pte_unmap_unlock(old_pte - 1, old_ptl);
178 if (need_rmap_locks)
179 drop_rmap_locks(vma);
180 }
181
182 #define LATENCY_LIMIT (64 * PAGE_SIZE)
183
184 unsigned long move_page_tables(struct vm_area_struct *vma,
185 unsigned long old_addr, struct vm_area_struct *new_vma,
186 unsigned long new_addr, unsigned long len,
187 bool need_rmap_locks)
188 {
189 unsigned long extent, next, old_end;
190 pmd_t *old_pmd, *new_pmd;
191 bool need_flush = false;
192 unsigned long mmun_start; /* For mmu_notifiers */
193 unsigned long mmun_end; /* For mmu_notifiers */
194
195 old_end = old_addr + len;
196 flush_cache_range(vma, old_addr, old_end);
197
198 mmun_start = old_addr;
199 mmun_end = old_end;
200 mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
201
202 for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
203 cond_resched();
204 next = (old_addr + PMD_SIZE) & PMD_MASK;
205 /* even if next overflowed, extent below will be ok */
206 extent = next - old_addr;
207 if (extent > old_end - old_addr)
208 extent = old_end - old_addr;
209 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
210 if (!old_pmd)
211 continue;
212 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
213 if (!new_pmd)
214 break;
215 if (pmd_trans_huge(*old_pmd)) {
216 if (extent == HPAGE_PMD_SIZE) {
217 bool moved;
218 /* See comment in move_ptes() */
219 if (need_rmap_locks)
220 take_rmap_locks(vma);
221 moved = move_huge_pmd(vma, old_addr, new_addr,
222 old_end, old_pmd, new_pmd,
223 &need_flush);
224 if (need_rmap_locks)
225 drop_rmap_locks(vma);
226 if (moved)
227 continue;
228 }
229 split_huge_pmd(vma, old_pmd, old_addr);
230 if (pmd_trans_unstable(old_pmd))
231 continue;
232 }
233 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr))
234 break;
235 next = (new_addr + PMD_SIZE) & PMD_MASK;
236 if (extent > next - new_addr)
237 extent = next - new_addr;
238 if (extent > LATENCY_LIMIT)
239 extent = LATENCY_LIMIT;
240 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
241 new_pmd, new_addr, need_rmap_locks, &need_flush);
242 }
243 if (need_flush)
244 flush_tlb_range(vma, old_end-len, old_addr);
245
246 mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
247
248 return len + old_addr - old_end; /* how much done */
249 }
250
251 static unsigned long move_vma(struct vm_area_struct *vma,
252 unsigned long old_addr, unsigned long old_len,
253 unsigned long new_len, unsigned long new_addr, bool *locked)
254 {
255 struct mm_struct *mm = vma->vm_mm;
256 struct vm_area_struct *new_vma;
257 unsigned long vm_flags = vma->vm_flags;
258 unsigned long new_pgoff;
259 unsigned long moved_len;
260 unsigned long excess = 0;
261 unsigned long hiwater_vm;
262 int split = 0;
263 int err;
264 bool need_rmap_locks;
265
266 /*
267 * We'd prefer to avoid failure later on in do_munmap:
268 * which may split one vma into three before unmapping.
269 */
270 if (mm->map_count >= sysctl_max_map_count - 3)
271 return -ENOMEM;
272
273 /*
274 * Advise KSM to break any KSM pages in the area to be moved:
275 * it would be confusing if they were to turn up at the new
276 * location, where they happen to coincide with different KSM
277 * pages recently unmapped. But leave vma->vm_flags as it was,
278 * so KSM can come around to merge on vma and new_vma afterwards.
279 */
280 err = ksm_madvise(vma, old_addr, old_addr + old_len,
281 MADV_UNMERGEABLE, &vm_flags);
282 if (err)
283 return err;
284
285 new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
286 new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
287 &need_rmap_locks);
288 if (!new_vma)
289 return -ENOMEM;
290
291 moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
292 need_rmap_locks);
293 if (moved_len < old_len) {
294 err = -ENOMEM;
295 } else if (vma->vm_ops && vma->vm_ops->mremap) {
296 err = vma->vm_ops->mremap(new_vma);
297 }
298
299 if (unlikely(err)) {
300 /*
301 * On error, move entries back from new area to old,
302 * which will succeed since page tables still there,
303 * and then proceed to unmap new area instead of old.
304 */
305 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
306 true);
307 vma = new_vma;
308 old_len = new_len;
309 old_addr = new_addr;
310 new_addr = err;
311 } else {
312 arch_remap(mm, old_addr, old_addr + old_len,
313 new_addr, new_addr + new_len);
314 }
315
316 /* Conceal VM_ACCOUNT so old reservation is not undone */
317 if (vm_flags & VM_ACCOUNT) {
318 vma->vm_flags &= ~VM_ACCOUNT;
319 excess = vma->vm_end - vma->vm_start - old_len;
320 if (old_addr > vma->vm_start &&
321 old_addr + old_len < vma->vm_end)
322 split = 1;
323 }
324
325 /*
326 * If we failed to move page tables we still do total_vm increment
327 * since do_munmap() will decrement it by old_len == new_len.
328 *
329 * Since total_vm is about to be raised artificially high for a
330 * moment, we need to restore high watermark afterwards: if stats
331 * are taken meanwhile, total_vm and hiwater_vm appear too high.
332 * If this were a serious issue, we'd add a flag to do_munmap().
333 */
334 hiwater_vm = mm->hiwater_vm;
335 vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
336
337 /* Tell pfnmap has moved from this vma */
338 if (unlikely(vma->vm_flags & VM_PFNMAP))
339 untrack_pfn_moved(vma);
340
341 if (do_munmap(mm, old_addr, old_len) < 0) {
342 /* OOM: unable to split vma, just get accounts right */
343 vm_unacct_memory(excess >> PAGE_SHIFT);
344 excess = 0;
345 }
346 mm->hiwater_vm = hiwater_vm;
347
348 /* Restore VM_ACCOUNT if one or two pieces of vma left */
349 if (excess) {
350 vma->vm_flags |= VM_ACCOUNT;
351 if (split)
352 vma->vm_next->vm_flags |= VM_ACCOUNT;
353 }
354
355 if (vm_flags & VM_LOCKED) {
356 mm->locked_vm += new_len >> PAGE_SHIFT;
357 *locked = true;
358 }
359
360 return new_addr;
361 }
362
363 static struct vm_area_struct *vma_to_resize(unsigned long addr,
364 unsigned long old_len, unsigned long new_len, unsigned long *p)
365 {
366 struct mm_struct *mm = current->mm;
367 struct vm_area_struct *vma = find_vma(mm, addr);
368 unsigned long pgoff;
369
370 if (!vma || vma->vm_start > addr)
371 return ERR_PTR(-EFAULT);
372
373 if (is_vm_hugetlb_page(vma))
374 return ERR_PTR(-EINVAL);
375
376 /* We can't remap across vm area boundaries */
377 if (old_len > vma->vm_end - addr)
378 return ERR_PTR(-EFAULT);
379
380 if (new_len == old_len)
381 return vma;
382
383 /* Need to be careful about a growing mapping */
384 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
385 pgoff += vma->vm_pgoff;
386 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
387 return ERR_PTR(-EINVAL);
388
389 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
390 return ERR_PTR(-EFAULT);
391
392 if (vma->vm_flags & VM_LOCKED) {
393 unsigned long locked, lock_limit;
394 locked = mm->locked_vm << PAGE_SHIFT;
395 lock_limit = rlimit(RLIMIT_MEMLOCK);
396 locked += new_len - old_len;
397 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
398 return ERR_PTR(-EAGAIN);
399 }
400
401 if (!may_expand_vm(mm, vma->vm_flags,
402 (new_len - old_len) >> PAGE_SHIFT))
403 return ERR_PTR(-ENOMEM);
404
405 if (vma->vm_flags & VM_ACCOUNT) {
406 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
407 if (security_vm_enough_memory_mm(mm, charged))
408 return ERR_PTR(-ENOMEM);
409 *p = charged;
410 }
411
412 return vma;
413 }
414
415 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
416 unsigned long new_addr, unsigned long new_len, bool *locked)
417 {
418 struct mm_struct *mm = current->mm;
419 struct vm_area_struct *vma;
420 unsigned long ret = -EINVAL;
421 unsigned long charged = 0;
422 unsigned long map_flags;
423
424 if (offset_in_page(new_addr))
425 goto out;
426
427 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
428 goto out;
429
430 /* Ensure the old/new locations do not overlap */
431 if (addr + old_len > new_addr && new_addr + new_len > addr)
432 goto out;
433
434 ret = do_munmap(mm, new_addr, new_len);
435 if (ret)
436 goto out;
437
438 if (old_len >= new_len) {
439 ret = do_munmap(mm, addr+new_len, old_len - new_len);
440 if (ret && old_len != new_len)
441 goto out;
442 old_len = new_len;
443 }
444
445 vma = vma_to_resize(addr, old_len, new_len, &charged);
446 if (IS_ERR(vma)) {
447 ret = PTR_ERR(vma);
448 goto out;
449 }
450
451 map_flags = MAP_FIXED;
452 if (vma->vm_flags & VM_MAYSHARE)
453 map_flags |= MAP_SHARED;
454
455 ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
456 ((addr - vma->vm_start) >> PAGE_SHIFT),
457 map_flags);
458 if (offset_in_page(ret))
459 goto out1;
460
461 ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
462 if (!(offset_in_page(ret)))
463 goto out;
464 out1:
465 vm_unacct_memory(charged);
466
467 out:
468 return ret;
469 }
470
471 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
472 {
473 unsigned long end = vma->vm_end + delta;
474 if (end < vma->vm_end) /* overflow */
475 return 0;
476 if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
477 return 0;
478 if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
479 0, MAP_FIXED) & ~PAGE_MASK)
480 return 0;
481 return 1;
482 }
483
484 /*
485 * Expand (or shrink) an existing mapping, potentially moving it at the
486 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
487 *
488 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
489 * This option implies MREMAP_MAYMOVE.
490 */
491 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
492 unsigned long, new_len, unsigned long, flags,
493 unsigned long, new_addr)
494 {
495 struct mm_struct *mm = current->mm;
496 struct vm_area_struct *vma;
497 unsigned long ret = -EINVAL;
498 unsigned long charged = 0;
499 bool locked = false;
500
501 if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
502 return ret;
503
504 if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
505 return ret;
506
507 if (offset_in_page(addr))
508 return ret;
509
510 old_len = PAGE_ALIGN(old_len);
511 new_len = PAGE_ALIGN(new_len);
512
513 /*
514 * We allow a zero old-len as a special case
515 * for DOS-emu "duplicate shm area" thing. But
516 * a zero new-len is nonsensical.
517 */
518 if (!new_len)
519 return ret;
520
521 if (down_write_killable(&current->mm->mmap_sem))
522 return -EINTR;
523
524 if (flags & MREMAP_FIXED) {
525 ret = mremap_to(addr, old_len, new_addr, new_len,
526 &locked);
527 goto out;
528 }
529
530 /*
531 * Always allow a shrinking remap: that just unmaps
532 * the unnecessary pages..
533 * do_munmap does all the needed commit accounting
534 */
535 if (old_len >= new_len) {
536 ret = do_munmap(mm, addr+new_len, old_len - new_len);
537 if (ret && old_len != new_len)
538 goto out;
539 ret = addr;
540 goto out;
541 }
542
543 /*
544 * Ok, we need to grow..
545 */
546 vma = vma_to_resize(addr, old_len, new_len, &charged);
547 if (IS_ERR(vma)) {
548 ret = PTR_ERR(vma);
549 goto out;
550 }
551
552 /* old_len exactly to the end of the area..
553 */
554 if (old_len == vma->vm_end - addr) {
555 /* can we just expand the current mapping? */
556 if (vma_expandable(vma, new_len - old_len)) {
557 int pages = (new_len - old_len) >> PAGE_SHIFT;
558
559 if (vma_adjust(vma, vma->vm_start, addr + new_len,
560 vma->vm_pgoff, NULL)) {
561 ret = -ENOMEM;
562 goto out;
563 }
564
565 vm_stat_account(mm, vma->vm_flags, pages);
566 if (vma->vm_flags & VM_LOCKED) {
567 mm->locked_vm += pages;
568 locked = true;
569 new_addr = addr;
570 }
571 ret = addr;
572 goto out;
573 }
574 }
575
576 /*
577 * We weren't able to just expand or shrink the area,
578 * we need to create a new one and move it..
579 */
580 ret = -ENOMEM;
581 if (flags & MREMAP_MAYMOVE) {
582 unsigned long map_flags = 0;
583 if (vma->vm_flags & VM_MAYSHARE)
584 map_flags |= MAP_SHARED;
585
586 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
587 vma->vm_pgoff +
588 ((addr - vma->vm_start) >> PAGE_SHIFT),
589 map_flags);
590 if (offset_in_page(new_addr)) {
591 ret = new_addr;
592 goto out;
593 }
594
595 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
596 }
597 out:
598 if (offset_in_page(ret)) {
599 vm_unacct_memory(charged);
600 locked = 0;
601 }
602 up_write(&current->mm->mmap_sem);
603 if (locked && new_len > old_len)
604 mm_populate(new_addr + old_len, new_len - old_len);
605 return ret;
606 }