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         start = untagged_addr(start);
  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
  59         /*
  60          * While get_vaddr_frames() could be used for transient (kernel
  61          * controlled lifetime) pinning of memory pages all current
  62          * users establish long term (userspace controlled lifetime)
  63          * page pinning. Treat get_vaddr_frames() like
  64          * get_user_pages_longterm() and disallow it for filesystem-dax
  65          * mappings.
  66          */
  67         if (vma_is_fsdax(vma)) {
  68                 ret = -EOPNOTSUPP;
  69                 goto out;
  70         }
  71
  72         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
  73                 vec->got_ref = true;
  74                 vec->is_pfns = false;
  75                 ret = get_user_pages_locked(start, nr_frames,
  76                         gup_flags, (struct page **)(vec->ptrs), &locked);
  77                 goto out;
  78         }
  79
  80         vec->got_ref = false;
  81         vec->is_pfns = true;
  82         do {
  83                 unsigned long *nums = frame_vector_pfns(vec);
  84
  85                 while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
  86                         err = follow_pfn(vma, start, &nums[ret]);
  87                         if (err) {
  88                                 if (ret == 0)
  89                                         ret = err;
  90                                 goto out;
  91                         }
  92                         start += PAGE_SIZE;
  93                         ret++;
  94                 }
  95                 /*
  96                  * We stop if we have enough pages or if VMA doesn't completely
  97                  * cover the tail page.
  98                  */
  99                 if (ret >= nr_frames || start < vma->vm_end)
 100                         break;
 101                 vma = find_vma_intersection(mm, start, start + 1);
 102         } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
 103 out:
 104         if (locked)
 105                 up_read(&mm->mmap_sem);
 106         if (!ret)
 107                 ret = -EFAULT;
 108         if (ret > 0)
 109                 vec->nr_frames = ret;
 110         return ret;
 111 }
 112 EXPORT_SYMBOL(get_vaddr_frames);
 113
 114 /**
 115  * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
 116  *                      them
 117  * @vec:        frame vector to put
 118  *
 119  * Drop references to pages if get_vaddr_frames() acquired them. We also
 120  * invalidate the frame vector so that it is prepared for the next call into
 121  * get_vaddr_frames().
 122  */
 123 void put_vaddr_frames(struct frame_vector *vec)
 124 {
 125         int i;
 126         struct page **pages;
 127
 128         if (!vec->got_ref)
 129                 goto out;
 130         pages = frame_vector_pages(vec);
 131         /*
 132          * frame_vector_pages() might needed to do a conversion when
 133          * get_vaddr_frames() got pages but vec was later converted to pfns.
 134          * But it shouldn't really fail to convert pfns back...
 135          */
 136         if (WARN_ON(IS_ERR(pages)))
 137                 goto out;
 138         for (i = 0; i < vec->nr_frames; i++)
 139                 put_page(pages[i]);
 140         vec->got_ref = false;
 141 out:
 142         vec->nr_frames = 0;
 143 }
 144 EXPORT_SYMBOL(put_vaddr_frames);
 145
 146 /**
 147  * frame_vector_to_pages - convert frame vector to contain page pointers
 148  * @vec:        frame vector to convert
 149  *
 150  * Convert @vec to contain array of page pointers.  If the conversion is
 151  * successful, return 0. Otherwise return an error. Note that we do not grab
 152  * page references for the page structures.
 153  */
 154 int frame_vector_to_pages(struct frame_vector *vec)
 155 {
 156         int i;
 157         unsigned long *nums;
 158         struct page **pages;
 159
 160         if (!vec->is_pfns)
 161                 return 0;
 162         nums = frame_vector_pfns(vec);
 163         for (i = 0; i < vec->nr_frames; i++)
 164                 if (!pfn_valid(nums[i]))
 165                         return -EINVAL;
 166         pages = (struct page **)nums;
 167         for (i = 0; i < vec->nr_frames; i++)
 168                 pages[i] = pfn_to_page(nums[i]);
 169         vec->is_pfns = false;
 170         return 0;
 171 }
 172 EXPORT_SYMBOL(frame_vector_to_pages);
 173
 174 /**
 175  * frame_vector_to_pfns - convert frame vector to contain pfns
 176  * @vec:        frame vector to convert
 177  *
 178  * Convert @vec to contain array of pfns.
 179  */
 180 void frame_vector_to_pfns(struct frame_vector *vec)
 181 {
 182         int i;
 183         unsigned long *nums;
 184         struct page **pages;
 185
 186         if (vec->is_pfns)
 187                 return;
 188         pages = (struct page **)(vec->ptrs);
 189         nums = (unsigned long *)pages;
 190         for (i = 0; i < vec->nr_frames; i++)
 191                 nums[i] = page_to_pfn(pages[i]);
 192         vec->is_pfns = true;
 193 }
 194 EXPORT_SYMBOL(frame_vector_to_pfns);
 195
 196 /**
 197  * frame_vector_create() - allocate & initialize structure for pinned pfns
 198  * @nr_frames:  number of pfns slots we should reserve
 199  *
 200  * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
 201  * pfns.
 202  */
 203 struct frame_vector *frame_vector_create(unsigned int nr_frames)
 204 {
 205         struct frame_vector *vec;
 206         int size = sizeof(struct frame_vector) + sizeof(void *) * nr_frames;
 207
 208         if (WARN_ON_ONCE(nr_frames == 0))
 209                 return NULL;
 210         /*
 211          * This is absurdly high. It's here just to avoid strange effects when
 212          * arithmetics overflows.
 213          */
 214         if (WARN_ON_ONCE(nr_frames > INT_MAX / sizeof(void *) / 2))
 215                 return NULL;
 216         /*
 217          * Avoid higher order allocations, use vmalloc instead. It should
 218          * be rare anyway.
 219          */
 220         vec = kvmalloc(size, GFP_KERNEL);
 221         if (!vec)
 222                 return NULL;
 223         vec->nr_allocated = nr_frames;
 224         vec->nr_frames = 0;
 225         return vec;
 226 }
 227 EXPORT_SYMBOL(frame_vector_create);
 228
 229 /**
 230  * frame_vector_destroy() - free memory allocated to carry frame vector
 231  * @vec:        Frame vector to free
 232  *
 233  * Free structure allocated by frame_vector_create() to carry frames.
 234  */
 235 void frame_vector_destroy(struct frame_vector *vec)
 236 {
 237         /* Make sure put_vaddr_frames() got called properly... */
 238         VM_BUG_ON(vec->nr_frames > 0);
 239         kvfree(vec);
 240 }
 241 EXPORT_SYMBOL(frame_vector_destroy);