xref: /openbmc/linux/mm/mremap.c (revision b830f94f)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *	mm/mremap.c
4  *
5  *	(C) Copyright 1996 Linus Torvalds
6  *
7  *	Address space accounting code	<alan@lxorguk.ukuu.org.uk>
8  *	(C) Copyright 2002 Red Hat Inc, All Rights Reserved
9  */
10 
11 #include <linux/mm.h>
12 #include <linux/hugetlb.h>
13 #include <linux/shm.h>
14 #include <linux/ksm.h>
15 #include <linux/mman.h>
16 #include <linux/swap.h>
17 #include <linux/capability.h>
18 #include <linux/fs.h>
19 #include <linux/swapops.h>
20 #include <linux/highmem.h>
21 #include <linux/security.h>
22 #include <linux/syscalls.h>
23 #include <linux/mmu_notifier.h>
24 #include <linux/uaccess.h>
25 #include <linux/mm-arch-hooks.h>
26 #include <linux/userfaultfd_k.h>
27 
28 #include <asm/cacheflush.h>
29 #include <asm/tlbflush.h>
30 
31 #include "internal.h"
32 
33 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
34 {
35 	pgd_t *pgd;
36 	p4d_t *p4d;
37 	pud_t *pud;
38 	pmd_t *pmd;
39 
40 	pgd = pgd_offset(mm, addr);
41 	if (pgd_none_or_clear_bad(pgd))
42 		return NULL;
43 
44 	p4d = p4d_offset(pgd, addr);
45 	if (p4d_none_or_clear_bad(p4d))
46 		return NULL;
47 
48 	pud = pud_offset(p4d, addr);
49 	if (pud_none_or_clear_bad(pud))
50 		return NULL;
51 
52 	pmd = pmd_offset(pud, addr);
53 	if (pmd_none(*pmd))
54 		return NULL;
55 
56 	return pmd;
57 }
58 
59 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
60 			    unsigned long addr)
61 {
62 	pgd_t *pgd;
63 	p4d_t *p4d;
64 	pud_t *pud;
65 	pmd_t *pmd;
66 
67 	pgd = pgd_offset(mm, addr);
68 	p4d = p4d_alloc(mm, pgd, addr);
69 	if (!p4d)
70 		return NULL;
71 	pud = pud_alloc(mm, p4d, addr);
72 	if (!pud)
73 		return NULL;
74 
75 	pmd = pmd_alloc(mm, pud, addr);
76 	if (!pmd)
77 		return NULL;
78 
79 	VM_BUG_ON(pmd_trans_huge(*pmd));
80 
81 	return pmd;
82 }
83 
84 static void take_rmap_locks(struct vm_area_struct *vma)
85 {
86 	if (vma->vm_file)
87 		i_mmap_lock_write(vma->vm_file->f_mapping);
88 	if (vma->anon_vma)
89 		anon_vma_lock_write(vma->anon_vma);
90 }
91 
92 static void drop_rmap_locks(struct vm_area_struct *vma)
93 {
94 	if (vma->anon_vma)
95 		anon_vma_unlock_write(vma->anon_vma);
96 	if (vma->vm_file)
97 		i_mmap_unlock_write(vma->vm_file->f_mapping);
98 }
99 
100 static pte_t move_soft_dirty_pte(pte_t pte)
101 {
102 	/*
103 	 * Set soft dirty bit so we can notice
104 	 * in userspace the ptes were moved.
105 	 */
106 #ifdef CONFIG_MEM_SOFT_DIRTY
107 	if (pte_present(pte))
108 		pte = pte_mksoft_dirty(pte);
109 	else if (is_swap_pte(pte))
110 		pte = pte_swp_mksoft_dirty(pte);
111 #endif
112 	return pte;
113 }
114 
115 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
116 		unsigned long old_addr, unsigned long old_end,
117 		struct vm_area_struct *new_vma, pmd_t *new_pmd,
118 		unsigned long new_addr, bool need_rmap_locks)
119 {
120 	struct mm_struct *mm = vma->vm_mm;
121 	pte_t *old_pte, *new_pte, pte;
122 	spinlock_t *old_ptl, *new_ptl;
123 	bool force_flush = false;
124 	unsigned long len = old_end - old_addr;
125 
126 	/*
127 	 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
128 	 * locks to ensure that rmap will always observe either the old or the
129 	 * new ptes. This is the easiest way to avoid races with
130 	 * truncate_pagecache(), page migration, etc...
131 	 *
132 	 * When need_rmap_locks is false, we use other ways to avoid
133 	 * such races:
134 	 *
135 	 * - During exec() shift_arg_pages(), we use a specially tagged vma
136 	 *   which rmap call sites look for using is_vma_temporary_stack().
137 	 *
138 	 * - During mremap(), new_vma is often known to be placed after vma
139 	 *   in rmap traversal order. This ensures rmap will always observe
140 	 *   either the old pte, or the new pte, or both (the page table locks
141 	 *   serialize access to individual ptes, but only rmap traversal
142 	 *   order guarantees that we won't miss both the old and new ptes).
143 	 */
144 	if (need_rmap_locks)
145 		take_rmap_locks(vma);
146 
147 	/*
148 	 * We don't have to worry about the ordering of src and dst
149 	 * pte locks because exclusive mmap_sem prevents deadlock.
150 	 */
151 	old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
152 	new_pte = pte_offset_map(new_pmd, new_addr);
153 	new_ptl = pte_lockptr(mm, new_pmd);
154 	if (new_ptl != old_ptl)
155 		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
156 	flush_tlb_batched_pending(vma->vm_mm);
157 	arch_enter_lazy_mmu_mode();
158 
159 	for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
160 				   new_pte++, new_addr += PAGE_SIZE) {
161 		if (pte_none(*old_pte))
162 			continue;
163 
164 		pte = ptep_get_and_clear(mm, old_addr, old_pte);
165 		/*
166 		 * If we are remapping a valid PTE, make sure
167 		 * to flush TLB before we drop the PTL for the
168 		 * PTE.
169 		 *
170 		 * NOTE! Both old and new PTL matter: the old one
171 		 * for racing with page_mkclean(), the new one to
172 		 * make sure the physical page stays valid until
173 		 * the TLB entry for the old mapping has been
174 		 * flushed.
175 		 */
176 		if (pte_present(pte))
177 			force_flush = true;
178 		pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
179 		pte = move_soft_dirty_pte(pte);
180 		set_pte_at(mm, new_addr, new_pte, pte);
181 	}
182 
183 	arch_leave_lazy_mmu_mode();
184 	if (force_flush)
185 		flush_tlb_range(vma, old_end - len, old_end);
186 	if (new_ptl != old_ptl)
187 		spin_unlock(new_ptl);
188 	pte_unmap(new_pte - 1);
189 	pte_unmap_unlock(old_pte - 1, old_ptl);
190 	if (need_rmap_locks)
191 		drop_rmap_locks(vma);
192 }
193 
194 #ifdef CONFIG_HAVE_MOVE_PMD
195 static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
196 		  unsigned long new_addr, unsigned long old_end,
197 		  pmd_t *old_pmd, pmd_t *new_pmd)
198 {
199 	spinlock_t *old_ptl, *new_ptl;
200 	struct mm_struct *mm = vma->vm_mm;
201 	pmd_t pmd;
202 
203 	if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK)
204 	    || old_end - old_addr < PMD_SIZE)
205 		return false;
206 
207 	/*
208 	 * The destination pmd shouldn't be established, free_pgtables()
209 	 * should have release it.
210 	 */
211 	if (WARN_ON(!pmd_none(*new_pmd)))
212 		return false;
213 
214 	/*
215 	 * We don't have to worry about the ordering of src and dst
216 	 * ptlocks because exclusive mmap_sem prevents deadlock.
217 	 */
218 	old_ptl = pmd_lock(vma->vm_mm, old_pmd);
219 	new_ptl = pmd_lockptr(mm, new_pmd);
220 	if (new_ptl != old_ptl)
221 		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
222 
223 	/* Clear the pmd */
224 	pmd = *old_pmd;
225 	pmd_clear(old_pmd);
226 
227 	VM_BUG_ON(!pmd_none(*new_pmd));
228 
229 	/* Set the new pmd */
230 	set_pmd_at(mm, new_addr, new_pmd, pmd);
231 	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
232 	if (new_ptl != old_ptl)
233 		spin_unlock(new_ptl);
234 	spin_unlock(old_ptl);
235 
236 	return true;
237 }
238 #endif
239 
240 unsigned long move_page_tables(struct vm_area_struct *vma,
241 		unsigned long old_addr, struct vm_area_struct *new_vma,
242 		unsigned long new_addr, unsigned long len,
243 		bool need_rmap_locks)
244 {
245 	unsigned long extent, next, old_end;
246 	struct mmu_notifier_range range;
247 	pmd_t *old_pmd, *new_pmd;
248 
249 	old_end = old_addr + len;
250 	flush_cache_range(vma, old_addr, old_end);
251 
252 	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
253 				old_addr, old_end);
254 	mmu_notifier_invalidate_range_start(&range);
255 
256 	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
257 		cond_resched();
258 		next = (old_addr + PMD_SIZE) & PMD_MASK;
259 		/* even if next overflowed, extent below will be ok */
260 		extent = next - old_addr;
261 		if (extent > old_end - old_addr)
262 			extent = old_end - old_addr;
263 		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
264 		if (!old_pmd)
265 			continue;
266 		new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
267 		if (!new_pmd)
268 			break;
269 		if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd)) {
270 			if (extent == HPAGE_PMD_SIZE) {
271 				bool moved;
272 				/* See comment in move_ptes() */
273 				if (need_rmap_locks)
274 					take_rmap_locks(vma);
275 				moved = move_huge_pmd(vma, old_addr, new_addr,
276 						    old_end, old_pmd, new_pmd);
277 				if (need_rmap_locks)
278 					drop_rmap_locks(vma);
279 				if (moved)
280 					continue;
281 			}
282 			split_huge_pmd(vma, old_pmd, old_addr);
283 			if (pmd_trans_unstable(old_pmd))
284 				continue;
285 		} else if (extent == PMD_SIZE) {
286 #ifdef CONFIG_HAVE_MOVE_PMD
287 			/*
288 			 * If the extent is PMD-sized, try to speed the move by
289 			 * moving at the PMD level if possible.
290 			 */
291 			bool moved;
292 
293 			if (need_rmap_locks)
294 				take_rmap_locks(vma);
295 			moved = move_normal_pmd(vma, old_addr, new_addr,
296 					old_end, old_pmd, new_pmd);
297 			if (need_rmap_locks)
298 				drop_rmap_locks(vma);
299 			if (moved)
300 				continue;
301 #endif
302 		}
303 
304 		if (pte_alloc(new_vma->vm_mm, new_pmd))
305 			break;
306 		next = (new_addr + PMD_SIZE) & PMD_MASK;
307 		if (extent > next - new_addr)
308 			extent = next - new_addr;
309 		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
310 			  new_pmd, new_addr, need_rmap_locks);
311 	}
312 
313 	mmu_notifier_invalidate_range_end(&range);
314 
315 	return len + old_addr - old_end;	/* how much done */
316 }
317 
318 static unsigned long move_vma(struct vm_area_struct *vma,
319 		unsigned long old_addr, unsigned long old_len,
320 		unsigned long new_len, unsigned long new_addr,
321 		bool *locked, struct vm_userfaultfd_ctx *uf,
322 		struct list_head *uf_unmap)
323 {
324 	struct mm_struct *mm = vma->vm_mm;
325 	struct vm_area_struct *new_vma;
326 	unsigned long vm_flags = vma->vm_flags;
327 	unsigned long new_pgoff;
328 	unsigned long moved_len;
329 	unsigned long excess = 0;
330 	unsigned long hiwater_vm;
331 	int split = 0;
332 	int err;
333 	bool need_rmap_locks;
334 
335 	/*
336 	 * We'd prefer to avoid failure later on in do_munmap:
337 	 * which may split one vma into three before unmapping.
338 	 */
339 	if (mm->map_count >= sysctl_max_map_count - 3)
340 		return -ENOMEM;
341 
342 	/*
343 	 * Advise KSM to break any KSM pages in the area to be moved:
344 	 * it would be confusing if they were to turn up at the new
345 	 * location, where they happen to coincide with different KSM
346 	 * pages recently unmapped.  But leave vma->vm_flags as it was,
347 	 * so KSM can come around to merge on vma and new_vma afterwards.
348 	 */
349 	err = ksm_madvise(vma, old_addr, old_addr + old_len,
350 						MADV_UNMERGEABLE, &vm_flags);
351 	if (err)
352 		return err;
353 
354 	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
355 	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
356 			   &need_rmap_locks);
357 	if (!new_vma)
358 		return -ENOMEM;
359 
360 	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
361 				     need_rmap_locks);
362 	if (moved_len < old_len) {
363 		err = -ENOMEM;
364 	} else if (vma->vm_ops && vma->vm_ops->mremap) {
365 		err = vma->vm_ops->mremap(new_vma);
366 	}
367 
368 	if (unlikely(err)) {
369 		/*
370 		 * On error, move entries back from new area to old,
371 		 * which will succeed since page tables still there,
372 		 * and then proceed to unmap new area instead of old.
373 		 */
374 		move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
375 				 true);
376 		vma = new_vma;
377 		old_len = new_len;
378 		old_addr = new_addr;
379 		new_addr = err;
380 	} else {
381 		mremap_userfaultfd_prep(new_vma, uf);
382 		arch_remap(mm, old_addr, old_addr + old_len,
383 			   new_addr, new_addr + new_len);
384 	}
385 
386 	/* Conceal VM_ACCOUNT so old reservation is not undone */
387 	if (vm_flags & VM_ACCOUNT) {
388 		vma->vm_flags &= ~VM_ACCOUNT;
389 		excess = vma->vm_end - vma->vm_start - old_len;
390 		if (old_addr > vma->vm_start &&
391 		    old_addr + old_len < vma->vm_end)
392 			split = 1;
393 	}
394 
395 	/*
396 	 * If we failed to move page tables we still do total_vm increment
397 	 * since do_munmap() will decrement it by old_len == new_len.
398 	 *
399 	 * Since total_vm is about to be raised artificially high for a
400 	 * moment, we need to restore high watermark afterwards: if stats
401 	 * are taken meanwhile, total_vm and hiwater_vm appear too high.
402 	 * If this were a serious issue, we'd add a flag to do_munmap().
403 	 */
404 	hiwater_vm = mm->hiwater_vm;
405 	vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
406 
407 	/* Tell pfnmap has moved from this vma */
408 	if (unlikely(vma->vm_flags & VM_PFNMAP))
409 		untrack_pfn_moved(vma);
410 
411 	if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
412 		/* OOM: unable to split vma, just get accounts right */
413 		vm_unacct_memory(excess >> PAGE_SHIFT);
414 		excess = 0;
415 	}
416 	mm->hiwater_vm = hiwater_vm;
417 
418 	/* Restore VM_ACCOUNT if one or two pieces of vma left */
419 	if (excess) {
420 		vma->vm_flags |= VM_ACCOUNT;
421 		if (split)
422 			vma->vm_next->vm_flags |= VM_ACCOUNT;
423 	}
424 
425 	if (vm_flags & VM_LOCKED) {
426 		mm->locked_vm += new_len >> PAGE_SHIFT;
427 		*locked = true;
428 	}
429 
430 	return new_addr;
431 }
432 
433 static struct vm_area_struct *vma_to_resize(unsigned long addr,
434 	unsigned long old_len, unsigned long new_len, unsigned long *p)
435 {
436 	struct mm_struct *mm = current->mm;
437 	struct vm_area_struct *vma = find_vma(mm, addr);
438 	unsigned long pgoff;
439 
440 	if (!vma || vma->vm_start > addr)
441 		return ERR_PTR(-EFAULT);
442 
443 	/*
444 	 * !old_len is a special case where an attempt is made to 'duplicate'
445 	 * a mapping.  This makes no sense for private mappings as it will
446 	 * instead create a fresh/new mapping unrelated to the original.  This
447 	 * is contrary to the basic idea of mremap which creates new mappings
448 	 * based on the original.  There are no known use cases for this
449 	 * behavior.  As a result, fail such attempts.
450 	 */
451 	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
452 		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
453 		return ERR_PTR(-EINVAL);
454 	}
455 
456 	if (is_vm_hugetlb_page(vma))
457 		return ERR_PTR(-EINVAL);
458 
459 	/* We can't remap across vm area boundaries */
460 	if (old_len > vma->vm_end - addr)
461 		return ERR_PTR(-EFAULT);
462 
463 	if (new_len == old_len)
464 		return vma;
465 
466 	/* Need to be careful about a growing mapping */
467 	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
468 	pgoff += vma->vm_pgoff;
469 	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
470 		return ERR_PTR(-EINVAL);
471 
472 	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
473 		return ERR_PTR(-EFAULT);
474 
475 	if (vma->vm_flags & VM_LOCKED) {
476 		unsigned long locked, lock_limit;
477 		locked = mm->locked_vm << PAGE_SHIFT;
478 		lock_limit = rlimit(RLIMIT_MEMLOCK);
479 		locked += new_len - old_len;
480 		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
481 			return ERR_PTR(-EAGAIN);
482 	}
483 
484 	if (!may_expand_vm(mm, vma->vm_flags,
485 				(new_len - old_len) >> PAGE_SHIFT))
486 		return ERR_PTR(-ENOMEM);
487 
488 	if (vma->vm_flags & VM_ACCOUNT) {
489 		unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
490 		if (security_vm_enough_memory_mm(mm, charged))
491 			return ERR_PTR(-ENOMEM);
492 		*p = charged;
493 	}
494 
495 	return vma;
496 }
497 
498 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
499 		unsigned long new_addr, unsigned long new_len, bool *locked,
500 		struct vm_userfaultfd_ctx *uf,
501 		struct list_head *uf_unmap_early,
502 		struct list_head *uf_unmap)
503 {
504 	struct mm_struct *mm = current->mm;
505 	struct vm_area_struct *vma;
506 	unsigned long ret = -EINVAL;
507 	unsigned long charged = 0;
508 	unsigned long map_flags;
509 
510 	if (offset_in_page(new_addr))
511 		goto out;
512 
513 	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
514 		goto out;
515 
516 	/* Ensure the old/new locations do not overlap */
517 	if (addr + old_len > new_addr && new_addr + new_len > addr)
518 		goto out;
519 
520 	/*
521 	 * move_vma() need us to stay 4 maps below the threshold, otherwise
522 	 * it will bail out at the very beginning.
523 	 * That is a problem if we have already unmaped the regions here
524 	 * (new_addr, and old_addr), because userspace will not know the
525 	 * state of the vma's after it gets -ENOMEM.
526 	 * So, to avoid such scenario we can pre-compute if the whole
527 	 * operation has high chances to success map-wise.
528 	 * Worst-scenario case is when both vma's (new_addr and old_addr) get
529 	 * split in 3 before unmaping it.
530 	 * That means 2 more maps (1 for each) to the ones we already hold.
531 	 * Check whether current map count plus 2 still leads us to 4 maps below
532 	 * the threshold, otherwise return -ENOMEM here to be more safe.
533 	 */
534 	if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
535 		return -ENOMEM;
536 
537 	ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
538 	if (ret)
539 		goto out;
540 
541 	if (old_len >= new_len) {
542 		ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
543 		if (ret && old_len != new_len)
544 			goto out;
545 		old_len = new_len;
546 	}
547 
548 	vma = vma_to_resize(addr, old_len, new_len, &charged);
549 	if (IS_ERR(vma)) {
550 		ret = PTR_ERR(vma);
551 		goto out;
552 	}
553 
554 	map_flags = MAP_FIXED;
555 	if (vma->vm_flags & VM_MAYSHARE)
556 		map_flags |= MAP_SHARED;
557 
558 	ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
559 				((addr - vma->vm_start) >> PAGE_SHIFT),
560 				map_flags);
561 	if (offset_in_page(ret))
562 		goto out1;
563 
564 	ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, uf,
565 		       uf_unmap);
566 	if (!(offset_in_page(ret)))
567 		goto out;
568 out1:
569 	vm_unacct_memory(charged);
570 
571 out:
572 	return ret;
573 }
574 
575 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
576 {
577 	unsigned long end = vma->vm_end + delta;
578 	if (end < vma->vm_end) /* overflow */
579 		return 0;
580 	if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
581 		return 0;
582 	if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
583 			      0, MAP_FIXED) & ~PAGE_MASK)
584 		return 0;
585 	return 1;
586 }
587 
588 /*
589  * Expand (or shrink) an existing mapping, potentially moving it at the
590  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
591  *
592  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
593  * This option implies MREMAP_MAYMOVE.
594  */
595 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
596 		unsigned long, new_len, unsigned long, flags,
597 		unsigned long, new_addr)
598 {
599 	struct mm_struct *mm = current->mm;
600 	struct vm_area_struct *vma;
601 	unsigned long ret = -EINVAL;
602 	unsigned long charged = 0;
603 	bool locked = false;
604 	bool downgraded = false;
605 	struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
606 	LIST_HEAD(uf_unmap_early);
607 	LIST_HEAD(uf_unmap);
608 
609 	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
610 		return ret;
611 
612 	if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
613 		return ret;
614 
615 	if (offset_in_page(addr))
616 		return ret;
617 
618 	old_len = PAGE_ALIGN(old_len);
619 	new_len = PAGE_ALIGN(new_len);
620 
621 	/*
622 	 * We allow a zero old-len as a special case
623 	 * for DOS-emu "duplicate shm area" thing. But
624 	 * a zero new-len is nonsensical.
625 	 */
626 	if (!new_len)
627 		return ret;
628 
629 	if (down_write_killable(&current->mm->mmap_sem))
630 		return -EINTR;
631 
632 	if (flags & MREMAP_FIXED) {
633 		ret = mremap_to(addr, old_len, new_addr, new_len,
634 				&locked, &uf, &uf_unmap_early, &uf_unmap);
635 		goto out;
636 	}
637 
638 	/*
639 	 * Always allow a shrinking remap: that just unmaps
640 	 * the unnecessary pages..
641 	 * __do_munmap does all the needed commit accounting, and
642 	 * downgrades mmap_sem to read if so directed.
643 	 */
644 	if (old_len >= new_len) {
645 		int retval;
646 
647 		retval = __do_munmap(mm, addr+new_len, old_len - new_len,
648 				  &uf_unmap, true);
649 		if (retval < 0 && old_len != new_len) {
650 			ret = retval;
651 			goto out;
652 		/* Returning 1 indicates mmap_sem is downgraded to read. */
653 		} else if (retval == 1)
654 			downgraded = true;
655 		ret = addr;
656 		goto out;
657 	}
658 
659 	/*
660 	 * Ok, we need to grow..
661 	 */
662 	vma = vma_to_resize(addr, old_len, new_len, &charged);
663 	if (IS_ERR(vma)) {
664 		ret = PTR_ERR(vma);
665 		goto out;
666 	}
667 
668 	/* old_len exactly to the end of the area..
669 	 */
670 	if (old_len == vma->vm_end - addr) {
671 		/* can we just expand the current mapping? */
672 		if (vma_expandable(vma, new_len - old_len)) {
673 			int pages = (new_len - old_len) >> PAGE_SHIFT;
674 
675 			if (vma_adjust(vma, vma->vm_start, addr + new_len,
676 				       vma->vm_pgoff, NULL)) {
677 				ret = -ENOMEM;
678 				goto out;
679 			}
680 
681 			vm_stat_account(mm, vma->vm_flags, pages);
682 			if (vma->vm_flags & VM_LOCKED) {
683 				mm->locked_vm += pages;
684 				locked = true;
685 				new_addr = addr;
686 			}
687 			ret = addr;
688 			goto out;
689 		}
690 	}
691 
692 	/*
693 	 * We weren't able to just expand or shrink the area,
694 	 * we need to create a new one and move it..
695 	 */
696 	ret = -ENOMEM;
697 	if (flags & MREMAP_MAYMOVE) {
698 		unsigned long map_flags = 0;
699 		if (vma->vm_flags & VM_MAYSHARE)
700 			map_flags |= MAP_SHARED;
701 
702 		new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
703 					vma->vm_pgoff +
704 					((addr - vma->vm_start) >> PAGE_SHIFT),
705 					map_flags);
706 		if (offset_in_page(new_addr)) {
707 			ret = new_addr;
708 			goto out;
709 		}
710 
711 		ret = move_vma(vma, addr, old_len, new_len, new_addr,
712 			       &locked, &uf, &uf_unmap);
713 	}
714 out:
715 	if (offset_in_page(ret)) {
716 		vm_unacct_memory(charged);
717 		locked = 0;
718 	}
719 	if (downgraded)
720 		up_read(&current->mm->mmap_sem);
721 	else
722 		up_write(&current->mm->mmap_sem);
723 	if (locked && new_len > old_len)
724 		mm_populate(new_addr + old_len, new_len - old_len);
725 	userfaultfd_unmap_complete(mm, &uf_unmap_early);
726 	mremap_userfaultfd_complete(&uf, addr, new_addr, old_len);
727 	userfaultfd_unmap_complete(mm, &uf_unmap);
728 	return ret;
729 }
730