vmscan: move isolate_lru_page() to vmscan.c
[linux-2.6.git] / mm / nommu.c
1 /*
2  *  linux/mm/nommu.c
3  *
4  *  Replacement code for mm functions to support CPU's that don't
5  *  have any form of memory management unit (thus no virtual memory).
6  *
7  *  See Documentation/nommu-mmap.txt
8  *
9  *  Copyright (c) 2004-2005 David Howells <dhowells@redhat.com>
10  *  Copyright (c) 2000-2003 David McCullough <davidm@snapgear.com>
11  *  Copyright (c) 2000-2001 D Jeff Dionne <jeff@uClinux.org>
12  *  Copyright (c) 2002      Greg Ungerer <gerg@snapgear.com>
13  *  Copyright (c) 2007      Paul Mundt <lethal@linux-sh.org>
14  */
15
16 #include <linux/module.h>
17 #include <linux/mm.h>
18 #include <linux/mman.h>
19 #include <linux/swap.h>
20 #include <linux/file.h>
21 #include <linux/highmem.h>
22 #include <linux/pagemap.h>
23 #include <linux/slab.h>
24 #include <linux/vmalloc.h>
25 #include <linux/tracehook.h>
26 #include <linux/blkdev.h>
27 #include <linux/backing-dev.h>
28 #include <linux/mount.h>
29 #include <linux/personality.h>
30 #include <linux/security.h>
31 #include <linux/syscalls.h>
32
33 #include <asm/uaccess.h>
34 #include <asm/tlb.h>
35 #include <asm/tlbflush.h>
36
37 void *high_memory;
38 struct page *mem_map;
39 unsigned long max_mapnr;
40 unsigned long num_physpages;
41 unsigned long askedalloc, realalloc;
42 atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
43 int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
44 int sysctl_overcommit_ratio = 50; /* default is 50% */
45 int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
46 int heap_stack_gap = 0;
47
48 EXPORT_SYMBOL(mem_map);
49 EXPORT_SYMBOL(num_physpages);
50
51 /* list of shareable VMAs */
52 struct rb_root nommu_vma_tree = RB_ROOT;
53 DECLARE_RWSEM(nommu_vma_sem);
54
55 struct vm_operations_struct generic_file_vm_ops = {
56 };
57
58 /*
59  * Handle all mappings that got truncated by a "truncate()"
60  * system call.
61  *
62  * NOTE! We have to be ready to update the memory sharing
63  * between the file and the memory map for a potential last
64  * incomplete page.  Ugly, but necessary.
65  */
66 int vmtruncate(struct inode *inode, loff_t offset)
67 {
68         struct address_space *mapping = inode->i_mapping;
69         unsigned long limit;
70
71         if (inode->i_size < offset)
72                 goto do_expand;
73         i_size_write(inode, offset);
74
75         truncate_inode_pages(mapping, offset);
76         goto out_truncate;
77
78 do_expand:
79         limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
80         if (limit != RLIM_INFINITY && offset > limit)
81                 goto out_sig;
82         if (offset > inode->i_sb->s_maxbytes)
83                 goto out;
84         i_size_write(inode, offset);
85
86 out_truncate:
87         if (inode->i_op && inode->i_op->truncate)
88                 inode->i_op->truncate(inode);
89         return 0;
90 out_sig:
91         send_sig(SIGXFSZ, current, 0);
92 out:
93         return -EFBIG;
94 }
95
96 EXPORT_SYMBOL(vmtruncate);
97
98 /*
99  * Return the total memory allocated for this pointer, not
100  * just what the caller asked for.
101  *
102  * Doesn't have to be accurate, i.e. may have races.
103  */
104 unsigned int kobjsize(const void *objp)
105 {
106         struct page *page;
107
108         /*
109          * If the object we have should not have ksize performed on it,
110          * return size of 0
111          */
112         if (!objp || !virt_addr_valid(objp))
113                 return 0;
114
115         page = virt_to_head_page(objp);
116
117         /*
118          * If the allocator sets PageSlab, we know the pointer came from
119          * kmalloc().
120          */
121         if (PageSlab(page))
122                 return ksize(objp);
123
124         /*
125          * The ksize() function is only guaranteed to work for pointers
126          * returned by kmalloc(). So handle arbitrary pointers here.
127          */
128         return PAGE_SIZE << compound_order(page);
129 }
130
131 /*
132  * get a list of pages in an address range belonging to the specified process
133  * and indicate the VMA that covers each page
134  * - this is potentially dodgy as we may end incrementing the page count of a
135  *   slab page or a secondary page from a compound page
136  * - don't permit access to VMAs that don't support it, such as I/O mappings
137  */
138 int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
139         unsigned long start, int len, int write, int force,
140         struct page **pages, struct vm_area_struct **vmas)
141 {
142         struct vm_area_struct *vma;
143         unsigned long vm_flags;
144         int i;
145
146         /* calculate required read or write permissions.
147          * - if 'force' is set, we only require the "MAY" flags.
148          */
149         vm_flags  = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
150         vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
151
152         for (i = 0; i < len; i++) {
153                 vma = find_vma(mm, start);
154                 if (!vma)
155                         goto finish_or_fault;
156
157                 /* protect what we can, including chardevs */
158                 if (vma->vm_flags & (VM_IO | VM_PFNMAP) ||
159                     !(vm_flags & vma->vm_flags))
160                         goto finish_or_fault;
161
162                 if (pages) {
163                         pages[i] = virt_to_page(start);
164                         if (pages[i])
165                                 page_cache_get(pages[i]);
166                 }
167                 if (vmas)
168                         vmas[i] = vma;
169                 start += PAGE_SIZE;
170         }
171
172         return i;
173
174 finish_or_fault:
175         return i ? : -EFAULT;
176 }
177 EXPORT_SYMBOL(get_user_pages);
178
179 DEFINE_RWLOCK(vmlist_lock);
180 struct vm_struct *vmlist;
181
182 void vfree(const void *addr)
183 {
184         kfree(addr);
185 }
186 EXPORT_SYMBOL(vfree);
187
188 void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot)
189 {
190         /*
191          *  You can't specify __GFP_HIGHMEM with kmalloc() since kmalloc()
192          * returns only a logical address.
193          */
194         return kmalloc(size, (gfp_mask | __GFP_COMP) & ~__GFP_HIGHMEM);
195 }
196 EXPORT_SYMBOL(__vmalloc);
197
198 void *vmalloc_user(unsigned long size)
199 {
200         void *ret;
201
202         ret = __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
203                         PAGE_KERNEL);
204         if (ret) {
205                 struct vm_area_struct *vma;
206
207                 down_write(&current->mm->mmap_sem);
208                 vma = find_vma(current->mm, (unsigned long)ret);
209                 if (vma)
210                         vma->vm_flags |= VM_USERMAP;
211                 up_write(&current->mm->mmap_sem);
212         }
213
214         return ret;
215 }
216 EXPORT_SYMBOL(vmalloc_user);
217
218 struct page *vmalloc_to_page(const void *addr)
219 {
220         return virt_to_page(addr);
221 }
222 EXPORT_SYMBOL(vmalloc_to_page);
223
224 unsigned long vmalloc_to_pfn(const void *addr)
225 {
226         return page_to_pfn(virt_to_page(addr));
227 }
228 EXPORT_SYMBOL(vmalloc_to_pfn);
229
230 long vread(char *buf, char *addr, unsigned long count)
231 {
232         memcpy(buf, addr, count);
233         return count;
234 }
235
236 long vwrite(char *buf, char *addr, unsigned long count)
237 {
238         /* Don't allow overflow */
239         if ((unsigned long) addr + count < count)
240                 count = -(unsigned long) addr;
241
242         memcpy(addr, buf, count);
243         return(count);
244 }
245
246 /*
247  *      vmalloc  -  allocate virtually continguos memory
248  *
249  *      @size:          allocation size
250  *
251  *      Allocate enough pages to cover @size from the page level
252  *      allocator and map them into continguos kernel virtual space.
253  *
254  *      For tight control over page level allocator and protection flags
255  *      use __vmalloc() instead.
256  */
257 void *vmalloc(unsigned long size)
258 {
259        return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL);
260 }
261 EXPORT_SYMBOL(vmalloc);
262
263 void *vmalloc_node(unsigned long size, int node)
264 {
265         return vmalloc(size);
266 }
267 EXPORT_SYMBOL(vmalloc_node);
268
269 #ifndef PAGE_KERNEL_EXEC
270 # define PAGE_KERNEL_EXEC PAGE_KERNEL
271 #endif
272
273 /**
274  *      vmalloc_exec  -  allocate virtually contiguous, executable memory
275  *      @size:          allocation size
276  *
277  *      Kernel-internal function to allocate enough pages to cover @size
278  *      the page level allocator and map them into contiguous and
279  *      executable kernel virtual space.
280  *
281  *      For tight control over page level allocator and protection flags
282  *      use __vmalloc() instead.
283  */
284
285 void *vmalloc_exec(unsigned long size)
286 {
287         return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC);
288 }
289
290 /**
291  * vmalloc_32  -  allocate virtually contiguous memory (32bit addressable)
292  *      @size:          allocation size
293  *
294  *      Allocate enough 32bit PA addressable pages to cover @size from the
295  *      page level allocator and map them into continguos kernel virtual space.
296  */
297 void *vmalloc_32(unsigned long size)
298 {
299         return __vmalloc(size, GFP_KERNEL, PAGE_KERNEL);
300 }
301 EXPORT_SYMBOL(vmalloc_32);
302
303 /**
304  * vmalloc_32_user - allocate zeroed virtually contiguous 32bit memory
305  *      @size:          allocation size
306  *
307  * The resulting memory area is 32bit addressable and zeroed so it can be
308  * mapped to userspace without leaking data.
309  *
310  * VM_USERMAP is set on the corresponding VMA so that subsequent calls to
311  * remap_vmalloc_range() are permissible.
312  */
313 void *vmalloc_32_user(unsigned long size)
314 {
315         /*
316          * We'll have to sort out the ZONE_DMA bits for 64-bit,
317          * but for now this can simply use vmalloc_user() directly.
318          */
319         return vmalloc_user(size);
320 }
321 EXPORT_SYMBOL(vmalloc_32_user);
322
323 void *vmap(struct page **pages, unsigned int count, unsigned long flags, pgprot_t prot)
324 {
325         BUG();
326         return NULL;
327 }
328 EXPORT_SYMBOL(vmap);
329
330 void vunmap(const void *addr)
331 {
332         BUG();
333 }
334 EXPORT_SYMBOL(vunmap);
335
336 /*
337  * Implement a stub for vmalloc_sync_all() if the architecture chose not to
338  * have one.
339  */
340 void  __attribute__((weak)) vmalloc_sync_all(void)
341 {
342 }
343
344 int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
345                    struct page *page)
346 {
347         return -EINVAL;
348 }
349 EXPORT_SYMBOL(vm_insert_page);
350
351 /*
352  *  sys_brk() for the most part doesn't need the global kernel
353  *  lock, except when an application is doing something nasty
354  *  like trying to un-brk an area that has already been mapped
355  *  to a regular file.  in this case, the unmapping will need
356  *  to invoke file system routines that need the global lock.
357  */
358 asmlinkage unsigned long sys_brk(unsigned long brk)
359 {
360         struct mm_struct *mm = current->mm;
361
362         if (brk < mm->start_brk || brk > mm->context.end_brk)
363                 return mm->brk;
364
365         if (mm->brk == brk)
366                 return mm->brk;
367
368         /*
369          * Always allow shrinking brk
370          */
371         if (brk <= mm->brk) {
372                 mm->brk = brk;
373                 return brk;
374         }
375
376         /*
377          * Ok, looks good - let it rip.
378          */
379         return mm->brk = brk;
380 }
381
382 #ifdef DEBUG
383 static void show_process_blocks(void)
384 {
385         struct vm_list_struct *vml;
386
387         printk("Process blocks %d:", current->pid);
388
389         for (vml = &current->mm->context.vmlist; vml; vml = vml->next) {
390                 printk(" %p: %p", vml, vml->vma);
391                 if (vml->vma)
392                         printk(" (%d @%lx #%d)",
393                                kobjsize((void *) vml->vma->vm_start),
394                                vml->vma->vm_start,
395                                atomic_read(&vml->vma->vm_usage));
396                 printk(vml->next ? " ->" : ".\n");
397         }
398 }
399 #endif /* DEBUG */
400
401 /*
402  * add a VMA into a process's mm_struct in the appropriate place in the list
403  * - should be called with mm->mmap_sem held writelocked
404  */
405 static void add_vma_to_mm(struct mm_struct *mm, struct vm_list_struct *vml)
406 {
407         struct vm_list_struct **ppv;
408
409         for (ppv = &current->mm->context.vmlist; *ppv; ppv = &(*ppv)->next)
410                 if ((*ppv)->vma->vm_start > vml->vma->vm_start)
411                         break;
412
413         vml->next = *ppv;
414         *ppv = vml;
415 }
416
417 /*
418  * look up the first VMA in which addr resides, NULL if none
419  * - should be called with mm->mmap_sem at least held readlocked
420  */
421 struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
422 {
423         struct vm_list_struct *loop, *vml;
424
425         /* search the vm_start ordered list */
426         vml = NULL;
427         for (loop = mm->context.vmlist; loop; loop = loop->next) {
428                 if (loop->vma->vm_start > addr)
429                         break;
430                 vml = loop;
431         }
432
433         if (vml && vml->vma->vm_end > addr)
434                 return vml->vma;
435
436         return NULL;
437 }
438 EXPORT_SYMBOL(find_vma);
439
440 /*
441  * find a VMA
442  * - we don't extend stack VMAs under NOMMU conditions
443  */
444 struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
445 {
446         return find_vma(mm, addr);
447 }
448
449 int expand_stack(struct vm_area_struct *vma, unsigned long address)
450 {
451         return -ENOMEM;
452 }
453
454 /*
455  * look up the first VMA exactly that exactly matches addr
456  * - should be called with mm->mmap_sem at least held readlocked
457  */
458 static inline struct vm_area_struct *find_vma_exact(struct mm_struct *mm,
459                                                     unsigned long addr)
460 {
461         struct vm_list_struct *vml;
462
463         /* search the vm_start ordered list */
464         for (vml = mm->context.vmlist; vml; vml = vml->next) {
465                 if (vml->vma->vm_start == addr)
466                         return vml->vma;
467                 if (vml->vma->vm_start > addr)
468                         break;
469         }
470
471         return NULL;
472 }
473
474 /*
475  * find a VMA in the global tree
476  */
477 static inline struct vm_area_struct *find_nommu_vma(unsigned long start)
478 {
479         struct vm_area_struct *vma;
480         struct rb_node *n = nommu_vma_tree.rb_node;
481
482         while (n) {
483                 vma = rb_entry(n, struct vm_area_struct, vm_rb);
484
485                 if (start < vma->vm_start)
486                         n = n->rb_left;
487                 else if (start > vma->vm_start)
488                         n = n->rb_right;
489                 else
490                         return vma;
491         }
492
493         return NULL;
494 }
495
496 /*
497  * add a VMA in the global tree
498  */
499 static void add_nommu_vma(struct vm_area_struct *vma)
500 {
501         struct vm_area_struct *pvma;
502         struct address_space *mapping;
503         struct rb_node **p = &nommu_vma_tree.rb_node;
504         struct rb_node *parent = NULL;
505
506         /* add the VMA to the mapping */
507         if (vma->vm_file) {
508                 mapping = vma->vm_file->f_mapping;
509
510                 flush_dcache_mmap_lock(mapping);
511                 vma_prio_tree_insert(vma, &mapping->i_mmap);
512                 flush_dcache_mmap_unlock(mapping);
513         }
514
515         /* add the VMA to the master list */
516         while (*p) {
517                 parent = *p;
518                 pvma = rb_entry(parent, struct vm_area_struct, vm_rb);
519
520                 if (vma->vm_start < pvma->vm_start) {
521                         p = &(*p)->rb_left;
522                 }
523                 else if (vma->vm_start > pvma->vm_start) {
524                         p = &(*p)->rb_right;
525                 }
526                 else {
527                         /* mappings are at the same address - this can only
528                          * happen for shared-mem chardevs and shared file
529                          * mappings backed by ramfs/tmpfs */
530                         BUG_ON(!(pvma->vm_flags & VM_SHARED));
531
532                         if (vma < pvma)
533                                 p = &(*p)->rb_left;
534                         else if (vma > pvma)
535                                 p = &(*p)->rb_right;
536                         else
537                                 BUG();
538                 }
539         }
540
541         rb_link_node(&vma->vm_rb, parent, p);
542         rb_insert_color(&vma->vm_rb, &nommu_vma_tree);
543 }
544
545 /*
546  * delete a VMA from the global list
547  */
548 static void delete_nommu_vma(struct vm_area_struct *vma)
549 {
550         struct address_space *mapping;
551
552         /* remove the VMA from the mapping */
553         if (vma->vm_file) {
554                 mapping = vma->vm_file->f_mapping;
555
556                 flush_dcache_mmap_lock(mapping);
557                 vma_prio_tree_remove(vma, &mapping->i_mmap);
558                 flush_dcache_mmap_unlock(mapping);
559         }
560
561         /* remove from the master list */
562         rb_erase(&vma->vm_rb, &nommu_vma_tree);
563 }
564
565 /*
566  * determine whether a mapping should be permitted and, if so, what sort of
567  * mapping we're capable of supporting
568  */
569 static int validate_mmap_request(struct file *file,
570                                  unsigned long addr,
571                                  unsigned long len,
572                                  unsigned long prot,
573                                  unsigned long flags,
574                                  unsigned long pgoff,
575                                  unsigned long *_capabilities)
576 {
577         unsigned long capabilities;
578         unsigned long reqprot = prot;
579         int ret;
580
581         /* do the simple checks first */
582         if (flags & MAP_FIXED || addr) {
583                 printk(KERN_DEBUG
584                        "%d: Can't do fixed-address/overlay mmap of RAM\n",
585                        current->pid);
586                 return -EINVAL;
587         }
588
589         if ((flags & MAP_TYPE) != MAP_PRIVATE &&
590             (flags & MAP_TYPE) != MAP_SHARED)
591                 return -EINVAL;
592
593         if (!len)
594                 return -EINVAL;
595
596         /* Careful about overflows.. */
597         len = PAGE_ALIGN(len);
598         if (!len || len > TASK_SIZE)
599                 return -ENOMEM;
600
601         /* offset overflow? */
602         if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
603                 return -EOVERFLOW;
604
605         if (file) {
606                 /* validate file mapping requests */
607                 struct address_space *mapping;
608
609                 /* files must support mmap */
610                 if (!file->f_op || !file->f_op->mmap)
611                         return -ENODEV;
612
613                 /* work out if what we've got could possibly be shared
614                  * - we support chardevs that provide their own "memory"
615                  * - we support files/blockdevs that are memory backed
616                  */
617                 mapping = file->f_mapping;
618                 if (!mapping)
619                         mapping = file->f_path.dentry->d_inode->i_mapping;
620
621                 capabilities = 0;
622                 if (mapping && mapping->backing_dev_info)
623                         capabilities = mapping->backing_dev_info->capabilities;
624
625                 if (!capabilities) {
626                         /* no explicit capabilities set, so assume some
627                          * defaults */
628                         switch (file->f_path.dentry->d_inode->i_mode & S_IFMT) {
629                         case S_IFREG:
630                         case S_IFBLK:
631                                 capabilities = BDI_CAP_MAP_COPY;
632                                 break;
633
634                         case S_IFCHR:
635                                 capabilities =
636                                         BDI_CAP_MAP_DIRECT |
637                                         BDI_CAP_READ_MAP |
638                                         BDI_CAP_WRITE_MAP;
639                                 break;
640
641                         default:
642                                 return -EINVAL;
643                         }
644                 }
645
646                 /* eliminate any capabilities that we can't support on this
647                  * device */
648                 if (!file->f_op->get_unmapped_area)
649                         capabilities &= ~BDI_CAP_MAP_DIRECT;
650                 if (!file->f_op->read)
651                         capabilities &= ~BDI_CAP_MAP_COPY;
652
653                 if (flags & MAP_SHARED) {
654                         /* do checks for writing, appending and locking */
655                         if ((prot & PROT_WRITE) &&
656                             !(file->f_mode & FMODE_WRITE))
657                                 return -EACCES;
658
659                         if (IS_APPEND(file->f_path.dentry->d_inode) &&
660                             (file->f_mode & FMODE_WRITE))
661                                 return -EACCES;
662
663                         if (locks_verify_locked(file->f_path.dentry->d_inode))
664                                 return -EAGAIN;
665
666                         if (!(capabilities & BDI_CAP_MAP_DIRECT))
667                                 return -ENODEV;
668
669                         if (((prot & PROT_READ)  && !(capabilities & BDI_CAP_READ_MAP))  ||
670                             ((prot & PROT_WRITE) && !(capabilities & BDI_CAP_WRITE_MAP)) ||
671                             ((prot & PROT_EXEC)  && !(capabilities & BDI_CAP_EXEC_MAP))
672                             ) {
673                                 printk("MAP_SHARED not completely supported on !MMU\n");
674                                 return -EINVAL;
675                         }
676
677                         /* we mustn't privatise shared mappings */
678                         capabilities &= ~BDI_CAP_MAP_COPY;
679                 }
680                 else {
681                         /* we're going to read the file into private memory we
682                          * allocate */
683                         if (!(capabilities & BDI_CAP_MAP_COPY))
684                                 return -ENODEV;
685
686                         /* we don't permit a private writable mapping to be
687                          * shared with the backing device */
688                         if (prot & PROT_WRITE)
689                                 capabilities &= ~BDI_CAP_MAP_DIRECT;
690                 }
691
692                 /* handle executable mappings and implied executable
693                  * mappings */
694                 if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
695                         if (prot & PROT_EXEC)
696                                 return -EPERM;
697                 }
698                 else if ((prot & PROT_READ) && !(prot & PROT_EXEC)) {
699                         /* handle implication of PROT_EXEC by PROT_READ */
700                         if (current->personality & READ_IMPLIES_EXEC) {
701                                 if (capabilities & BDI_CAP_EXEC_MAP)
702                                         prot |= PROT_EXEC;
703                         }
704                 }
705                 else if ((prot & PROT_READ) &&
706                          (prot & PROT_EXEC) &&
707                          !(capabilities & BDI_CAP_EXEC_MAP)
708                          ) {
709                         /* backing file is not executable, try to copy */
710                         capabilities &= ~BDI_CAP_MAP_DIRECT;
711                 }
712         }
713         else {
714                 /* anonymous mappings are always memory backed and can be
715                  * privately mapped
716                  */
717                 capabilities = BDI_CAP_MAP_COPY;
718
719                 /* handle PROT_EXEC implication by PROT_READ */
720                 if ((prot & PROT_READ) &&
721                     (current->personality & READ_IMPLIES_EXEC))
722                         prot |= PROT_EXEC;
723         }
724
725         /* allow the security API to have its say */
726         ret = security_file_mmap(file, reqprot, prot, flags, addr, 0);
727         if (ret < 0)
728                 return ret;
729
730         /* looks okay */
731         *_capabilities = capabilities;
732         return 0;
733 }
734
735 /*
736  * we've determined that we can make the mapping, now translate what we
737  * now know into VMA flags
738  */
739 static unsigned long determine_vm_flags(struct file *file,
740                                         unsigned long prot,
741                                         unsigned long flags,
742                                         unsigned long capabilities)
743 {
744         unsigned long vm_flags;
745
746         vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags);
747         vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
748         /* vm_flags |= mm->def_flags; */
749
750         if (!(capabilities & BDI_CAP_MAP_DIRECT)) {
751                 /* attempt to share read-only copies of mapped file chunks */
752                 if (file && !(prot & PROT_WRITE))
753                         vm_flags |= VM_MAYSHARE;
754         }
755         else {
756                 /* overlay a shareable mapping on the backing device or inode
757                  * if possible - used for chardevs, ramfs/tmpfs/shmfs and
758                  * romfs/cramfs */
759                 if (flags & MAP_SHARED)
760                         vm_flags |= VM_MAYSHARE | VM_SHARED;
761                 else if ((((vm_flags & capabilities) ^ vm_flags) & BDI_CAP_VMFLAGS) == 0)
762                         vm_flags |= VM_MAYSHARE;
763         }
764
765         /* refuse to let anyone share private mappings with this process if
766          * it's being traced - otherwise breakpoints set in it may interfere
767          * with another untraced process
768          */
769         if ((flags & MAP_PRIVATE) && tracehook_expect_breakpoints(current))
770                 vm_flags &= ~VM_MAYSHARE;
771
772         return vm_flags;
773 }
774
775 /*
776  * set up a shared mapping on a file
777  */
778 static int do_mmap_shared_file(struct vm_area_struct *vma, unsigned long len)
779 {
780         int ret;
781
782         ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
783         if (ret != -ENOSYS)
784                 return ret;
785
786         /* getting an ENOSYS error indicates that direct mmap isn't
787          * possible (as opposed to tried but failed) so we'll fall
788          * through to making a private copy of the data and mapping
789          * that if we can */
790         return -ENODEV;
791 }
792
793 /*
794  * set up a private mapping or an anonymous shared mapping
795  */
796 static int do_mmap_private(struct vm_area_struct *vma, unsigned long len)
797 {
798         void *base;
799         int ret;
800
801         /* invoke the file's mapping function so that it can keep track of
802          * shared mappings on devices or memory
803          * - VM_MAYSHARE will be set if it may attempt to share
804          */
805         if (vma->vm_file) {
806                 ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
807                 if (ret != -ENOSYS) {
808                         /* shouldn't return success if we're not sharing */
809                         BUG_ON(ret == 0 && !(vma->vm_flags & VM_MAYSHARE));
810                         return ret; /* success or a real error */
811                 }
812
813                 /* getting an ENOSYS error indicates that direct mmap isn't
814                  * possible (as opposed to tried but failed) so we'll try to
815                  * make a private copy of the data and map that instead */
816         }
817
818         /* allocate some memory to hold the mapping
819          * - note that this may not return a page-aligned address if the object
820          *   we're allocating is smaller than a page
821          */
822         base = kmalloc(len, GFP_KERNEL|__GFP_COMP);
823         if (!base)
824                 goto enomem;
825
826         vma->vm_start = (unsigned long) base;
827         vma->vm_end = vma->vm_start + len;
828         vma->vm_flags |= VM_MAPPED_COPY;
829
830 #ifdef WARN_ON_SLACK
831         if (len + WARN_ON_SLACK <= kobjsize(result))
832                 printk("Allocation of %lu bytes from process %d has %lu bytes of slack\n",
833                        len, current->pid, kobjsize(result) - len);
834 #endif
835
836         if (vma->vm_file) {
837                 /* read the contents of a file into the copy */
838                 mm_segment_t old_fs;
839                 loff_t fpos;
840
841                 fpos = vma->vm_pgoff;
842                 fpos <<= PAGE_SHIFT;
843
844                 old_fs = get_fs();
845                 set_fs(KERNEL_DS);
846                 ret = vma->vm_file->f_op->read(vma->vm_file, base, len, &fpos);
847                 set_fs(old_fs);
848
849                 if (ret < 0)
850                         goto error_free;
851
852                 /* clear the last little bit */
853                 if (ret < len)
854                         memset(base + ret, 0, len - ret);
855
856         } else {
857                 /* if it's an anonymous mapping, then just clear it */
858                 memset(base, 0, len);
859         }
860
861         return 0;
862
863 error_free:
864         kfree(base);
865         vma->vm_start = 0;
866         return ret;
867
868 enomem:
869         printk("Allocation of length %lu from process %d failed\n",
870                len, current->pid);
871         show_free_areas();
872         return -ENOMEM;
873 }
874
875 /*
876  * handle mapping creation for uClinux
877  */
878 unsigned long do_mmap_pgoff(struct file *file,
879                             unsigned long addr,
880                             unsigned long len,
881                             unsigned long prot,
882                             unsigned long flags,
883                             unsigned long pgoff)
884 {
885         struct vm_list_struct *vml = NULL;
886         struct vm_area_struct *vma = NULL;
887         struct rb_node *rb;
888         unsigned long capabilities, vm_flags;
889         void *result;
890         int ret;
891
892         if (!(flags & MAP_FIXED))
893                 addr = round_hint_to_min(addr);
894
895         /* decide whether we should attempt the mapping, and if so what sort of
896          * mapping */
897         ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,
898                                     &capabilities);
899         if (ret < 0)
900                 return ret;
901
902         /* we've determined that we can make the mapping, now translate what we
903          * now know into VMA flags */
904         vm_flags = determine_vm_flags(file, prot, flags, capabilities);
905
906         /* we're going to need to record the mapping if it works */
907         vml = kzalloc(sizeof(struct vm_list_struct), GFP_KERNEL);
908         if (!vml)
909                 goto error_getting_vml;
910
911         down_write(&nommu_vma_sem);
912
913         /* if we want to share, we need to check for VMAs created by other
914          * mmap() calls that overlap with our proposed mapping
915          * - we can only share with an exact match on most regular files
916          * - shared mappings on character devices and memory backed files are
917          *   permitted to overlap inexactly as far as we are concerned for in
918          *   these cases, sharing is handled in the driver or filesystem rather
919          *   than here
920          */
921         if (vm_flags & VM_MAYSHARE) {
922                 unsigned long pglen = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
923                 unsigned long vmpglen;
924
925                 /* suppress VMA sharing for shared regions */
926                 if (vm_flags & VM_SHARED &&
927                     capabilities & BDI_CAP_MAP_DIRECT)
928                         goto dont_share_VMAs;
929
930                 for (rb = rb_first(&nommu_vma_tree); rb; rb = rb_next(rb)) {
931                         vma = rb_entry(rb, struct vm_area_struct, vm_rb);
932
933                         if (!(vma->vm_flags & VM_MAYSHARE))
934                                 continue;
935
936                         /* search for overlapping mappings on the same file */
937                         if (vma->vm_file->f_path.dentry->d_inode != file->f_path.dentry->d_inode)
938                                 continue;
939
940                         if (vma->vm_pgoff >= pgoff + pglen)
941                                 continue;
942
943                         vmpglen = vma->vm_end - vma->vm_start + PAGE_SIZE - 1;
944                         vmpglen >>= PAGE_SHIFT;
945                         if (pgoff >= vma->vm_pgoff + vmpglen)
946                                 continue;
947
948                         /* handle inexactly overlapping matches between mappings */
949                         if (vma->vm_pgoff != pgoff || vmpglen != pglen) {
950                                 if (!(capabilities & BDI_CAP_MAP_DIRECT))
951                                         goto sharing_violation;
952                                 continue;
953                         }
954
955                         /* we've found a VMA we can share */
956                         atomic_inc(&vma->vm_usage);
957
958                         vml->vma = vma;
959                         result = (void *) vma->vm_start;
960                         goto shared;
961                 }
962
963         dont_share_VMAs:
964                 vma = NULL;
965
966                 /* obtain the address at which to make a shared mapping
967                  * - this is the hook for quasi-memory character devices to
968                  *   tell us the location of a shared mapping
969                  */
970                 if (file && file->f_op->get_unmapped_area) {
971                         addr = file->f_op->get_unmapped_area(file, addr, len,
972                                                              pgoff, flags);
973                         if (IS_ERR((void *) addr)) {
974                                 ret = addr;
975                                 if (ret != (unsigned long) -ENOSYS)
976                                         goto error;
977
978                                 /* the driver refused to tell us where to site
979                                  * the mapping so we'll have to attempt to copy
980                                  * it */
981                                 ret = (unsigned long) -ENODEV;
982                                 if (!(capabilities & BDI_CAP_MAP_COPY))
983                                         goto error;
984
985                                 capabilities &= ~BDI_CAP_MAP_DIRECT;
986                         }
987                 }
988         }
989
990         /* we're going to need a VMA struct as well */
991         vma = kzalloc(sizeof(struct vm_area_struct), GFP_KERNEL);
992         if (!vma)
993                 goto error_getting_vma;
994
995         INIT_LIST_HEAD(&vma->anon_vma_node);
996         atomic_set(&vma->vm_usage, 1);
997         if (file) {
998                 get_file(file);
999                 if (vm_flags & VM_EXECUTABLE) {
1000                         added_exe_file_vma(current->mm);
1001                         vma->vm_mm = current->mm;
1002                 }
1003         }
1004         vma->vm_file    = file;
1005         vma->vm_flags   = vm_flags;
1006         vma->vm_start   = addr;
1007         vma->vm_end     = addr + len;
1008         vma->vm_pgoff   = pgoff;
1009
1010         vml->vma = vma;
1011
1012         /* set up the mapping */
1013         if (file && vma->vm_flags & VM_SHARED)
1014                 ret = do_mmap_shared_file(vma, len);
1015         else
1016                 ret = do_mmap_private(vma, len);
1017         if (ret < 0)
1018                 goto error;
1019
1020         /* okay... we have a mapping; now we have to register it */
1021         result = (void *) vma->vm_start;
1022
1023         if (vma->vm_flags & VM_MAPPED_COPY) {
1024                 realalloc += kobjsize(result);
1025                 askedalloc += len;
1026         }
1027
1028         realalloc += kobjsize(vma);
1029         askedalloc += sizeof(*vma);
1030
1031         current->mm->total_vm += len >> PAGE_SHIFT;
1032
1033         add_nommu_vma(vma);
1034
1035  shared:
1036         realalloc += kobjsize(vml);
1037         askedalloc += sizeof(*vml);
1038
1039         add_vma_to_mm(current->mm, vml);
1040
1041         up_write(&nommu_vma_sem);
1042
1043         if (prot & PROT_EXEC)
1044                 flush_icache_range((unsigned long) result,
1045                                    (unsigned long) result + len);
1046
1047 #ifdef DEBUG
1048         printk("do_mmap:\n");
1049         show_process_blocks();
1050 #endif
1051
1052         return (unsigned long) result;
1053
1054  error:
1055         up_write(&nommu_vma_sem);
1056         kfree(vml);
1057         if (vma) {
1058                 if (vma->vm_file) {
1059                         fput(vma->vm_file);
1060                         if (vma->vm_flags & VM_EXECUTABLE)
1061                                 removed_exe_file_vma(vma->vm_mm);
1062                 }
1063                 kfree(vma);
1064         }
1065         return ret;
1066
1067  sharing_violation:
1068         up_write(&nommu_vma_sem);
1069         printk("Attempt to share mismatched mappings\n");
1070         kfree(vml);
1071         return -EINVAL;
1072
1073  error_getting_vma:
1074         up_write(&nommu_vma_sem);
1075         kfree(vml);
1076         printk("Allocation of vma for %lu byte allocation from process %d failed\n",
1077                len, current->pid);
1078         show_free_areas();
1079         return -ENOMEM;
1080
1081  error_getting_vml:
1082         printk("Allocation of vml for %lu byte allocation from process %d failed\n",
1083                len, current->pid);
1084         show_free_areas();
1085         return -ENOMEM;
1086 }
1087 EXPORT_SYMBOL(do_mmap_pgoff);
1088
1089 /*
1090  * handle mapping disposal for uClinux
1091  */
1092 static void put_vma(struct mm_struct *mm, struct vm_area_struct *vma)
1093 {
1094         if (vma) {
1095                 down_write(&nommu_vma_sem);
1096
1097                 if (atomic_dec_and_test(&vma->vm_usage)) {
1098                         delete_nommu_vma(vma);
1099
1100                         if (vma->vm_ops && vma->vm_ops->close)
1101                                 vma->vm_ops->close(vma);
1102
1103                         /* IO memory and memory shared directly out of the pagecache from
1104                          * ramfs/tmpfs mustn't be released here */
1105                         if (vma->vm_flags & VM_MAPPED_COPY) {
1106                                 realalloc -= kobjsize((void *) vma->vm_start);
1107                                 askedalloc -= vma->vm_end - vma->vm_start;
1108                                 kfree((void *) vma->vm_start);
1109                         }
1110
1111                         realalloc -= kobjsize(vma);
1112                         askedalloc -= sizeof(*vma);
1113
1114                         if (vma->vm_file) {
1115                                 fput(vma->vm_file);
1116                                 if (vma->vm_flags & VM_EXECUTABLE)
1117                                         removed_exe_file_vma(mm);
1118                         }
1119                         kfree(vma);
1120                 }
1121
1122                 up_write(&nommu_vma_sem);
1123         }
1124 }
1125
1126 /*
1127  * release a mapping
1128  * - under NOMMU conditions the parameters must match exactly to the mapping to
1129  *   be removed
1130  */
1131 int do_munmap(struct mm_struct *mm, unsigned long addr, size_t len)
1132 {
1133         struct vm_list_struct *vml, **parent;
1134         unsigned long end = addr + len;
1135
1136 #ifdef DEBUG
1137         printk("do_munmap:\n");
1138 #endif
1139
1140         for (parent = &mm->context.vmlist; *parent; parent = &(*parent)->next) {
1141                 if ((*parent)->vma->vm_start > addr)
1142                         break;
1143                 if ((*parent)->vma->vm_start == addr &&
1144                     ((len == 0) || ((*parent)->vma->vm_end == end)))
1145                         goto found;
1146         }
1147
1148         printk("munmap of non-mmaped memory by process %d (%s): %p\n",
1149                current->pid, current->comm, (void *) addr);
1150         return -EINVAL;
1151
1152  found:
1153         vml = *parent;
1154
1155         put_vma(mm, vml->vma);
1156
1157         *parent = vml->next;
1158         realalloc -= kobjsize(vml);
1159         askedalloc -= sizeof(*vml);
1160         kfree(vml);
1161
1162         update_hiwater_vm(mm);
1163         mm->total_vm -= len >> PAGE_SHIFT;
1164
1165 #ifdef DEBUG
1166         show_process_blocks();
1167 #endif
1168
1169         return 0;
1170 }
1171 EXPORT_SYMBOL(do_munmap);
1172
1173 asmlinkage long sys_munmap(unsigned long addr, size_t len)
1174 {
1175         int ret;
1176         struct mm_struct *mm = current->mm;
1177
1178         down_write(&mm->mmap_sem);
1179         ret = do_munmap(mm, addr, len);
1180         up_write(&mm->mmap_sem);
1181         return ret;
1182 }
1183
1184 /*
1185  * Release all mappings
1186  */
1187 void exit_mmap(struct mm_struct * mm)
1188 {
1189         struct vm_list_struct *tmp;
1190
1191         if (mm) {
1192 #ifdef DEBUG
1193                 printk("Exit_mmap:\n");
1194 #endif
1195
1196                 mm->total_vm = 0;
1197
1198                 while ((tmp = mm->context.vmlist)) {
1199                         mm->context.vmlist = tmp->next;
1200                         put_vma(mm, tmp->vma);
1201
1202                         realalloc -= kobjsize(tmp);
1203                         askedalloc -= sizeof(*tmp);
1204                         kfree(tmp);
1205                 }
1206
1207 #ifdef DEBUG
1208                 show_process_blocks();
1209 #endif
1210         }
1211 }
1212
1213 unsigned long do_brk(unsigned long addr, unsigned long len)
1214 {
1215         return -ENOMEM;
1216 }
1217
1218 /*
1219  * expand (or shrink) an existing mapping, potentially moving it at the same
1220  * time (controlled by the MREMAP_MAYMOVE flag and available VM space)
1221  *
1222  * under NOMMU conditions, we only permit changing a mapping's size, and only
1223  * as long as it stays within the hole allocated by the kmalloc() call in
1224  * do_mmap_pgoff() and the block is not shareable
1225  *
1226  * MREMAP_FIXED is not supported under NOMMU conditions
1227  */
1228 unsigned long do_mremap(unsigned long addr,
1229                         unsigned long old_len, unsigned long new_len,
1230                         unsigned long flags, unsigned long new_addr)
1231 {
1232         struct vm_area_struct *vma;
1233
1234         /* insanity checks first */
1235         if (new_len == 0)
1236                 return (unsigned long) -EINVAL;
1237
1238         if (flags & MREMAP_FIXED && new_addr != addr)
1239                 return (unsigned long) -EINVAL;
1240
1241         vma = find_vma_exact(current->mm, addr);
1242         if (!vma)
1243                 return (unsigned long) -EINVAL;
1244
1245         if (vma->vm_end != vma->vm_start + old_len)
1246                 return (unsigned long) -EFAULT;
1247
1248         if (vma->vm_flags & VM_MAYSHARE)
1249                 return (unsigned long) -EPERM;
1250
1251         if (new_len > kobjsize((void *) addr))
1252                 return (unsigned long) -ENOMEM;
1253
1254         /* all checks complete - do it */
1255         vma->vm_end = vma->vm_start + new_len;
1256
1257         askedalloc -= old_len;
1258         askedalloc += new_len;
1259
1260         return vma->vm_start;
1261 }
1262 EXPORT_SYMBOL(do_mremap);
1263
1264 asmlinkage unsigned long sys_mremap(unsigned long addr,
1265         unsigned long old_len, unsigned long new_len,
1266         unsigned long flags, unsigned long new_addr)
1267 {
1268         unsigned long ret;
1269
1270         down_write(&current->mm->mmap_sem);
1271         ret = do_mremap(addr, old_len, new_len, flags, new_addr);
1272         up_write(&current->mm->mmap_sem);
1273         return ret;
1274 }
1275
1276 struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
1277                         unsigned int foll_flags)
1278 {
1279         return NULL;
1280 }
1281
1282 int remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
1283                 unsigned long to, unsigned long size, pgprot_t prot)
1284 {
1285         vma->vm_start = vma->vm_pgoff << PAGE_SHIFT;
1286         return 0;
1287 }
1288 EXPORT_SYMBOL(remap_pfn_range);
1289
1290 int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
1291                         unsigned long pgoff)
1292 {
1293         unsigned int size = vma->vm_end - vma->vm_start;
1294
1295         if (!(vma->vm_flags & VM_USERMAP))
1296                 return -EINVAL;
1297
1298         vma->vm_start = (unsigned long)(addr + (pgoff << PAGE_SHIFT));
1299         vma->vm_end = vma->vm_start + size;
1300
1301         return 0;
1302 }
1303 EXPORT_SYMBOL(remap_vmalloc_range);
1304
1305 void swap_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
1306 {
1307 }
1308
1309 unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
1310         unsigned long len, unsigned long pgoff, unsigned long flags)
1311 {
1312         return -ENOMEM;
1313 }
1314
1315 void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
1316 {
1317 }
1318
1319 void unmap_mapping_range(struct address_space *mapping,
1320                          loff_t const holebegin, loff_t const holelen,
1321                          int even_cows)
1322 {
1323 }
1324 EXPORT_SYMBOL(unmap_mapping_range);
1325
1326 /*
1327  * ask for an unmapped area at which to create a mapping on a file
1328  */
1329 unsigned long get_unmapped_area(struct file *file, unsigned long addr,
1330                                 unsigned long len, unsigned long pgoff,
1331                                 unsigned long flags)
1332 {
1333         unsigned long (*get_area)(struct file *, unsigned long, unsigned long,
1334                                   unsigned long, unsigned long);
1335
1336         get_area = current->mm->get_unmapped_area;
1337         if (file && file->f_op && file->f_op->get_unmapped_area)
1338                 get_area = file->f_op->get_unmapped_area;
1339
1340         if (!get_area)
1341                 return -ENOSYS;
1342
1343         return get_area(file, addr, len, pgoff, flags);
1344 }
1345 EXPORT_SYMBOL(get_unmapped_area);
1346
1347 /*
1348  * Check that a process has enough memory to allocate a new virtual
1349  * mapping. 0 means there is enough memory for the allocation to
1350  * succeed and -ENOMEM implies there is not.
1351  *
1352  * We currently support three overcommit policies, which are set via the
1353  * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting
1354  *
1355  * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
1356  * Additional code 2002 Jul 20 by Robert Love.
1357  *
1358  * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
1359  *
1360  * Note this is a helper function intended to be used by LSMs which
1361  * wish to use this logic.
1362  */
1363 int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
1364 {
1365         unsigned long free, allowed;
1366
1367         vm_acct_memory(pages);
1368
1369         /*
1370          * Sometimes we want to use more memory than we have
1371          */
1372         if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
1373                 return 0;
1374
1375         if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
1376                 unsigned long n;
1377
1378                 free = global_page_state(NR_FILE_PAGES);
1379                 free += nr_swap_pages;
1380
1381                 /*
1382                  * Any slabs which are created with the
1383                  * SLAB_RECLAIM_ACCOUNT flag claim to have contents
1384                  * which are reclaimable, under pressure.  The dentry
1385                  * cache and most inode caches should fall into this
1386                  */
1387                 free += global_page_state(NR_SLAB_RECLAIMABLE);
1388
1389                 /*
1390                  * Leave the last 3% for root
1391                  */
1392                 if (!cap_sys_admin)
1393                         free -= free / 32;
1394
1395                 if (free > pages)
1396                         return 0;
1397
1398                 /*
1399                  * nr_free_pages() is very expensive on large systems,
1400                  * only call if we're about to fail.
1401                  */
1402                 n = nr_free_pages();
1403
1404                 /*
1405                  * Leave reserved pages. The pages are not for anonymous pages.
1406                  */
1407                 if (n <= totalreserve_pages)
1408                         goto error;
1409                 else
1410                         n -= totalreserve_pages;
1411
1412                 /*
1413                  * Leave the last 3% for root
1414                  */
1415                 if (!cap_sys_admin)
1416                         n -= n / 32;
1417                 free += n;
1418
1419                 if (free > pages)
1420                         return 0;
1421
1422                 goto error;
1423         }
1424
1425         allowed = totalram_pages * sysctl_overcommit_ratio / 100;
1426         /*
1427          * Leave the last 3% for root
1428          */
1429         if (!cap_sys_admin)
1430                 allowed -= allowed / 32;
1431         allowed += total_swap_pages;
1432
1433         /* Don't let a single process grow too big:
1434            leave 3% of the size of this process for other processes */
1435         allowed -= current->mm->total_vm / 32;
1436
1437         /*
1438          * cast `allowed' as a signed long because vm_committed_space
1439          * sometimes has a negative value
1440          */
1441         if (atomic_long_read(&vm_committed_space) < (long)allowed)
1442                 return 0;
1443 error:
1444         vm_unacct_memory(pages);
1445
1446         return -ENOMEM;
1447 }
1448
1449 int in_gate_area_no_task(unsigned long addr)
1450 {
1451         return 0;
1452 }
1453
1454 int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1455 {
1456         BUG();
1457         return 0;
1458 }
1459 EXPORT_SYMBOL(filemap_fault);
1460
1461 /*
1462  * Access another process' address space.
1463  * - source/target buffer must be kernel space
1464  */
1465 int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
1466 {
1467         struct vm_area_struct *vma;
1468         struct mm_struct *mm;
1469
1470         if (addr + len < addr)
1471                 return 0;
1472
1473         mm = get_task_mm(tsk);
1474         if (!mm)
1475                 return 0;
1476
1477         down_read(&mm->mmap_sem);
1478
1479         /* the access must start within one of the target process's mappings */
1480         vma = find_vma(mm, addr);
1481         if (vma) {
1482                 /* don't overrun this mapping */
1483                 if (addr + len >= vma->vm_end)
1484                         len = vma->vm_end - addr;
1485
1486                 /* only read or write mappings where it is permitted */
1487                 if (write && vma->vm_flags & VM_MAYWRITE)
1488                         len -= copy_to_user((void *) addr, buf, len);
1489                 else if (!write && vma->vm_flags & VM_MAYREAD)
1490                         len -= copy_from_user(buf, (void *) addr, len);
1491                 else
1492                         len = 0;
1493         } else {
1494                 len = 0;
1495         }
1496
1497         up_read(&mm->mmap_sem);
1498         mmput(mm);
1499         return len;
1500 }