mm/frame_vector.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/kernel.h>
   3 #include <linux/errno.h>
   4 #include <linux/err.h>
   5 #include <linux/mm.h>
   6 #include <linux/slab.h>
   7 #include <linux/vmalloc.h>
   8 #include <linux/pagemap.h>
   9 #include <linux/sched.h>
  10
  11 /**
  12  * get_vaddr_frames() - map virtual addresses to pfns
  13  * @start:      starting user address
  14  * @nr_frames:  number of pages / pfns from start to map
  15  * @gup_flags:  flags modifying lookup behaviour
  16  * @vec:        structure which receives pages / pfns of the addresses mapped.
  17  *              It should have space for at least nr_frames entries.
  18  *
  19  * This function maps virtual addresses from @start and fills @vec structure
  20  * with page frame numbers or page pointers to corresponding pages (choice
  21  * depends on the type of the vma underlying the virtual address). If @start
  22  * belongs to a normal vma, the function grabs reference to each of the pages
  23  * to pin them in memory. If @start belongs to VM_IO | VM_PFNMAP vma, we don't
  24  * touch page structures and the caller must make sure pfns aren't reused for
  25  * anything else while he is using them.
  26  *
  27  * The function returns number of pages mapped which may be less than
  28  * @nr_frames. In particular we stop mapping if there are more vmas of
  29  * different type underlying the specified range of virtual addresses.
  30  * When the function isn't able to map a single page, it returns error.
  31  *
  32  * This function takes care of grabbing mmap_sem as necessary.
  33  */
  34 int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
  35                      unsigned int gup_flags, struct frame_vector *vec)
  36 {
  37         struct mm_struct *mm = current->mm;
  38         struct vm_area_struct *vma;
  39         int ret = 0;
  40         int err;
  41         int locked;
  42
  43         if (nr_frames == 0)
  44                 return 0;
  45
  46         if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
  47                 nr_frames = vec->nr_allocated;
  48
  49         down_read(&mm->mmap_sem);
  50         locked = 1;
  51         vma = find_vma_intersection(mm, start, start + 1);
  52         if (!vma) {
  53                 ret = -EFAULT;
  54                 goto out;
  55         }
  56         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
  57                 vec->got_ref = true;
  58                 vec->is_pfns = false;
  59                 ret = get_user_pages_locked(start, nr_frames,
  60                         gup_flags, (struct page **)(vec->ptrs), &locked);
  61                 goto out;
  62         }
  63
  64         vec->got_ref = false;
  65         vec->is_pfns = true;
  66         do {
  67                 unsigned long *nums = frame_vector_pfns(vec);
  68
  69                 while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
  70                         err = follow_pfn(vma, start, &nums[ret]);
  71                         if (err) {
  72                                 if (ret == 0)
  73                                         ret = err;
  74                                 goto out;
  75                         }
  76                         start += PAGE_SIZE;
  77                         ret++;
  78                 }
  79                 /*
  80                  * We stop if we have enough pages or if VMA doesn't completely
  81                  * cover the tail page.
  82                  */
  83                 if (ret >= nr_frames || start < vma->vm_end)
  84                         break;
  85                 vma = find_vma_intersection(mm, start, start + 1);
  86         } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
  87 out:
  88         if (locked)
  89                 up_read(&mm->mmap_sem);
  90         if (!ret)
  91                 ret = -EFAULT;
  92         if (ret > 0)
  93                 vec->nr_frames = ret;
  94         return ret;
  95 }
  96 EXPORT_SYMBOL(get_vaddr_frames);
  97
  98 /**
  99  * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
 100  *                      them
 101  * @vec:        frame vector to put
 102  *
 103  * Drop references to pages if get_vaddr_frames() acquired them. We also
 104  * invalidate the frame vector so that it is prepared for the next call into
 105  * get_vaddr_frames().
 106  */
 107 void put_vaddr_frames(struct frame_vector *vec)
 108 {
 109         int i;
 110         struct page **pages;
 111
 112         if (!vec->got_ref)
 113                 goto out;
 114         pages = frame_vector_pages(vec);
 115         /*
 116          * frame_vector_pages() might needed to do a conversion when
 117          * get_vaddr_frames() got pages but vec was later converted to pfns.
 118          * But it shouldn't really fail to convert pfns back...
 119          */
 120         if (WARN_ON(IS_ERR(pages)))
 121                 goto out;
 122         for (i = 0; i < vec->nr_frames; i++)
 123                 put_page(pages[i]);
 124         vec->got_ref = false;
 125 out:
 126         vec->nr_frames = 0;
 127 }
 128 EXPORT_SYMBOL(put_vaddr_frames);
 129
 130 /**
 131  * frame_vector_to_pages - convert frame vector to contain page pointers
 132  * @vec:        frame vector to convert
 133  *
 134  * Convert @vec to contain array of page pointers.  If the conversion is
 135  * successful, return 0. Otherwise return an error. Note that we do not grab
 136  * page references for the page structures.
 137  */
 138 int frame_vector_to_pages(struct frame_vector *vec)
 139 {
 140         int i;
 141         unsigned long *nums;
 142         struct page **pages;
 143
 144         if (!vec->is_pfns)
 145                 return 0;
 146         nums = frame_vector_pfns(vec);
 147         for (i = 0; i < vec->nr_frames; i++)
 148                 if (!pfn_valid(nums[i]))
 149                         return -EINVAL;
 150         pages = (struct page **)nums;
 151         for (i = 0; i < vec->nr_frames; i++)
 152                 pages[i] = pfn_to_page(nums[i]);
 153         vec->is_pfns = false;
 154         return 0;
 155 }
 156 EXPORT_SYMBOL(frame_vector_to_pages);
 157
 158 /**
 159  * frame_vector_to_pfns - convert frame vector to contain pfns
 160  * @vec:        frame vector to convert
 161  *
 162  * Convert @vec to contain array of pfns.
 163  */
 164 void frame_vector_to_pfns(struct frame_vector *vec)
 165 {
 166         int i;
 167         unsigned long *nums;
 168         struct page **pages;
 169
 170         if (vec->is_pfns)
 171                 return;
 172         pages = (struct page **)(vec->ptrs);
 173         nums = (unsigned long *)pages;
 174         for (i = 0; i < vec->nr_frames; i++)
 175                 nums[i] = page_to_pfn(pages[i]);
 176         vec->is_pfns = true;
 177 }
 178 EXPORT_SYMBOL(frame_vector_to_pfns);
 179
 180 /**
 181  * frame_vector_create() - allocate & initialize structure for pinned pfns
 182  * @nr_frames:  number of pfns slots we should reserve
 183  *
 184  * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
 185  * pfns.
 186  */
 187 struct frame_vector *frame_vector_create(unsigned int nr_frames)
 188 {
 189         struct frame_vector *vec;
 190         int size = sizeof(struct frame_vector) + sizeof(void *) * nr_frames;
 191
 192         if (WARN_ON_ONCE(nr_frames == 0))
 193                 return NULL;
 194         /*
 195          * This is absurdly high. It's here just to avoid strange effects when
 196          * arithmetics overflows.
 197          */
 198         if (WARN_ON_ONCE(nr_frames > INT_MAX / sizeof(void *) / 2))
 199                 return NULL;
 200         /*
 201          * Avoid higher order allocations, use vmalloc instead. It should
 202          * be rare anyway.
 203          */
 204         vec = kvmalloc(size, GFP_KERNEL);
 205         if (!vec)
 206                 return NULL;
 207         vec->nr_allocated = nr_frames;
 208         vec->nr_frames = 0;
 209         return vec;
 210 }
 211 EXPORT_SYMBOL(frame_vector_create);
 212
 213 /**
 214  * frame_vector_destroy() - free memory allocated to carry frame vector
 215  * @vec:        Frame vector to free
 216  *
 217  * Free structure allocated by frame_vector_create() to carry frames.
 218  */
 219 void frame_vector_destroy(struct frame_vector *vec)
 220 {
 221         /* Make sure put_vaddr_frames() got called properly... */
 222         VM_BUG_ON(vec->nr_frames > 0);
 223         kvfree(vec);
 224 }
 225 EXPORT_SYMBOL(frame_vector_destroy);