mm/frame_vector.c

   1 #include <linux/kernel.h>
   2 #include <linux/errno.h>
   3 #include <linux/err.h>
   4 #include <linux/mm.h>
   5 #include <linux/slab.h>
   6 #include <linux/vmalloc.h>
   7 #include <linux/pagemap.h>
   8 #include <linux/sched.h>
   9
  10 /**
  11  * get_vaddr_frames() - map virtual addresses to pfns
  12  * @start:      starting user address
  13  * @nr_frames:  number of pages / pfns from start to map
  14  * @write:      whether pages will be written to by the caller
  15  * @force:      whether to force write access even if user mapping is
  16  *              readonly. See description of the same argument of
  17                 get_user_pages().
  18  * @vec:        structure which receives pages / pfns of the addresses mapped.
  19  *              It should have space for at least nr_frames entries.
  20  *
  21  * This function maps virtual addresses from @start and fills @vec structure
  22  * with page frame numbers or page pointers to corresponding pages (choice
  23  * depends on the type of the vma underlying the virtual address). If @start
  24  * belongs to a normal vma, the function grabs reference to each of the pages
  25  * to pin them in memory. If @start belongs to VM_IO | VM_PFNMAP vma, we don't
  26  * touch page structures and the caller must make sure pfns aren't reused for
  27  * anything else while he is using them.
  28  *
  29  * The function returns number of pages mapped which may be less than
  30  * @nr_frames. In particular we stop mapping if there are more vmas of
  31  * different type underlying the specified range of virtual addresses.
  32  * When the function isn't able to map a single page, it returns error.
  33  *
  34  * This function takes care of grabbing mmap_sem as necessary.
  35  */
  36 int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
  37                      bool write, bool force, struct frame_vector *vec)
  38 {
  39         struct mm_struct *mm = current->mm;
  40         struct vm_area_struct *vma;
  41         int ret = 0;
  42         int err;
  43         int locked;
  44
  45         if (nr_frames == 0)
  46                 return 0;
  47
  48         if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
  49                 nr_frames = vec->nr_allocated;
  50
  51         down_read(&mm->mmap_sem);
  52         locked = 1;
  53         vma = find_vma_intersection(mm, start, start + 1);
  54         if (!vma) {
  55                 ret = -EFAULT;
  56                 goto out;
  57         }
  58         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
  59                 vec->got_ref = true;
  60                 vec->is_pfns = false;
  61                 ret = get_user_pages_locked(current, mm, start, nr_frames,
  62                         write, force, (struct page **)(vec->ptrs), &locked);
  63                 goto out;
  64         }
  65
  66         vec->got_ref = false;
  67         vec->is_pfns = true;
  68         do {
  69                 unsigned long *nums = frame_vector_pfns(vec);
  70
  71                 while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
  72                         err = follow_pfn(vma, start, &nums[ret]);
  73                         if (err) {
  74                                 if (ret == 0)
  75                                         ret = err;
  76                                 goto out;
  77                         }
  78                         start += PAGE_SIZE;
  79                         ret++;
  80                 }
  81                 /*
  82                  * We stop if we have enough pages or if VMA doesn't completely
  83                  * cover the tail page.
  84                  */
  85                 if (ret >= nr_frames || start < vma->vm_end)
  86                         break;
  87                 vma = find_vma_intersection(mm, start, start + 1);
  88         } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
  89 out:
  90         if (locked)
  91                 up_read(&mm->mmap_sem);
  92         if (!ret)
  93                 ret = -EFAULT;
  94         if (ret > 0)
  95                 vec->nr_frames = ret;
  96         return ret;
  97 }
  98 EXPORT_SYMBOL(get_vaddr_frames);
  99
 100 /**
 101  * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
 102  *                      them
 103  * @vec:        frame vector to put
 104  *
 105  * Drop references to pages if get_vaddr_frames() acquired them. We also
 106  * invalidate the frame vector so that it is prepared for the next call into
 107  * get_vaddr_frames().
 108  */
 109 void put_vaddr_frames(struct frame_vector *vec)
 110 {
 111         int i;
 112         struct page **pages;
 113
 114         if (!vec->got_ref)
 115                 goto out;
 116         pages = frame_vector_pages(vec);
 117         /*
 118          * frame_vector_pages() might needed to do a conversion when
 119          * get_vaddr_frames() got pages but vec was later converted to pfns.
 120          * But it shouldn't really fail to convert pfns back...
 121          */
 122         if (WARN_ON(IS_ERR(pages)))
 123                 goto out;
 124         for (i = 0; i < vec->nr_frames; i++)
 125                 put_page(pages[i]);
 126         vec->got_ref = false;
 127 out:
 128         vec->nr_frames = 0;
 129 }
 130 EXPORT_SYMBOL(put_vaddr_frames);
 131
 132 /**
 133  * frame_vector_to_pages - convert frame vector to contain page pointers
 134  * @vec:        frame vector to convert
 135  *
 136  * Convert @vec to contain array of page pointers.  If the conversion is
 137  * successful, return 0. Otherwise return an error. Note that we do not grab
 138  * page references for the page structures.
 139  */
 140 int frame_vector_to_pages(struct frame_vector *vec)
 141 {
 142         int i;
 143         unsigned long *nums;
 144         struct page **pages;
 145
 146         if (!vec->is_pfns)
 147                 return 0;
 148         nums = frame_vector_pfns(vec);
 149         for (i = 0; i < vec->nr_frames; i++)
 150                 if (!pfn_valid(nums[i]))
 151                         return -EINVAL;
 152         pages = (struct page **)nums;
 153         for (i = 0; i < vec->nr_frames; i++)
 154                 pages[i] = pfn_to_page(nums[i]);
 155         vec->is_pfns = false;
 156         return 0;
 157 }
 158 EXPORT_SYMBOL(frame_vector_to_pages);
 159
 160 /**
 161  * frame_vector_to_pfns - convert frame vector to contain pfns
 162  * @vec:        frame vector to convert
 163  *
 164  * Convert @vec to contain array of pfns.
 165  */
 166 void frame_vector_to_pfns(struct frame_vector *vec)
 167 {
 168         int i;
 169         unsigned long *nums;
 170         struct page **pages;
 171
 172         if (vec->is_pfns)
 173                 return;
 174         pages = (struct page **)(vec->ptrs);
 175         nums = (unsigned long *)pages;
 176         for (i = 0; i < vec->nr_frames; i++)
 177                 nums[i] = page_to_pfn(pages[i]);
 178         vec->is_pfns = true;
 179 }
 180 EXPORT_SYMBOL(frame_vector_to_pfns);
 181
 182 /**
 183  * frame_vector_create() - allocate & initialize structure for pinned pfns
 184  * @nr_frames:  number of pfns slots we should reserve
 185  *
 186  * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
 187  * pfns.
 188  */
 189 struct frame_vector *frame_vector_create(unsigned int nr_frames)
 190 {
 191         struct frame_vector *vec;
 192         int size = sizeof(struct frame_vector) + sizeof(void *) * nr_frames;
 193
 194         if (WARN_ON_ONCE(nr_frames == 0))
 195                 return NULL;
 196         /*
 197          * This is absurdly high. It's here just to avoid strange effects when
 198          * arithmetics overflows.
 199          */
 200         if (WARN_ON_ONCE(nr_frames > INT_MAX / sizeof(void *) / 2))
 201                 return NULL;
 202         /*
 203          * Avoid higher order allocations, use vmalloc instead. It should
 204          * be rare anyway.
 205          */
 206         if (size <= PAGE_SIZE)
 207                 vec = kmalloc(size, GFP_KERNEL);
 208         else
 209                 vec = vmalloc(size);
 210         if (!vec)
 211                 return NULL;
 212         vec->nr_allocated = nr_frames;
 213         vec->nr_frames = 0;
 214         return vec;
 215 }
 216 EXPORT_SYMBOL(frame_vector_create);
 217
 218 /**
 219  * frame_vector_destroy() - free memory allocated to carry frame vector
 220  * @vec:        Frame vector to free
 221  *
 222  * Free structure allocated by frame_vector_create() to carry frames.
 223  */
 224 void frame_vector_destroy(struct frame_vector *vec)
 225 {
 226         /* Make sure put_vaddr_frames() got called properly... */
 227         VM_BUG_ON(vec->nr_frames > 0);
 228         kvfree(vec);
 229 }
 230 EXPORT_SYMBOL(frame_vector_destroy);