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
  57         /*
  58          * While get_vaddr_frames() could be used for transient (kernel
  59          * controlled lifetime) pinning of memory pages all current
  60          * users establish long term (userspace controlled lifetime)
  61          * page pinning. Treat get_vaddr_frames() like
  62          * get_user_pages_longterm() and disallow it for filesystem-dax
  63          * mappings.
  64          */
  65         if (vma_is_fsdax(vma))
  66                 return -EOPNOTSUPP;
  67
  68         if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
  69                 vec->got_ref = true;
  70                 vec->is_pfns = false;
  71                 ret = get_user_pages_locked(start, nr_frames,
  72                         gup_flags, (struct page **)(vec->ptrs), &locked);
  73                 goto out;
  74         }
  75
  76         vec->got_ref = false;
  77         vec->is_pfns = true;
  78         do {
  79                 unsigned long *nums = frame_vector_pfns(vec);
  80
  81                 while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
  82                         err = follow_pfn(vma, start, &nums[ret]);
  83                         if (err) {
  84                                 if (ret == 0)
  85                                         ret = err;
  86                                 goto out;
  87                         }
  88                         start += PAGE_SIZE;
  89                         ret++;
  90                 }
  91                 /*
  92                  * We stop if we have enough pages or if VMA doesn't completely
  93                  * cover the tail page.
  94                  */
  95                 if (ret >= nr_frames || start < vma->vm_end)
  96                         break;
  97                 vma = find_vma_intersection(mm, start, start + 1);
  98         } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
  99 out:
 100         if (locked)
 101                 up_read(&mm->mmap_sem);
 102         if (!ret)
 103                 ret = -EFAULT;
 104         if (ret > 0)
 105                 vec->nr_frames = ret;
 106         return ret;
 107 }
 108 EXPORT_SYMBOL(get_vaddr_frames);
 109
 110 /**
 111  * put_vaddr_frames() - drop references to pages if get_vaddr_frames() acquired
 112  *                      them
 113  * @vec:        frame vector to put
 114  *
 115  * Drop references to pages if get_vaddr_frames() acquired them. We also
 116  * invalidate the frame vector so that it is prepared for the next call into
 117  * get_vaddr_frames().
 118  */
 119 void put_vaddr_frames(struct frame_vector *vec)
 120 {
 121         int i;
 122         struct page **pages;
 123
 124         if (!vec->got_ref)
 125                 goto out;
 126         pages = frame_vector_pages(vec);
 127         /*
 128          * frame_vector_pages() might needed to do a conversion when
 129          * get_vaddr_frames() got pages but vec was later converted to pfns.
 130          * But it shouldn't really fail to convert pfns back...
 131          */
 132         if (WARN_ON(IS_ERR(pages)))
 133                 goto out;
 134         for (i = 0; i < vec->nr_frames; i++)
 135                 put_page(pages[i]);
 136         vec->got_ref = false;
 137 out:
 138         vec->nr_frames = 0;
 139 }
 140 EXPORT_SYMBOL(put_vaddr_frames);
 141
 142 /**
 143  * frame_vector_to_pages - convert frame vector to contain page pointers
 144  * @vec:        frame vector to convert
 145  *
 146  * Convert @vec to contain array of page pointers.  If the conversion is
 147  * successful, return 0. Otherwise return an error. Note that we do not grab
 148  * page references for the page structures.
 149  */
 150 int frame_vector_to_pages(struct frame_vector *vec)
 151 {
 152         int i;
 153         unsigned long *nums;
 154         struct page **pages;
 155
 156         if (!vec->is_pfns)
 157                 return 0;
 158         nums = frame_vector_pfns(vec);
 159         for (i = 0; i < vec->nr_frames; i++)
 160                 if (!pfn_valid(nums[i]))
 161                         return -EINVAL;
 162         pages = (struct page **)nums;
 163         for (i = 0; i < vec->nr_frames; i++)
 164                 pages[i] = pfn_to_page(nums[i]);
 165         vec->is_pfns = false;
 166         return 0;
 167 }
 168 EXPORT_SYMBOL(frame_vector_to_pages);
 169
 170 /**
 171  * frame_vector_to_pfns - convert frame vector to contain pfns
 172  * @vec:        frame vector to convert
 173  *
 174  * Convert @vec to contain array of pfns.
 175  */
 176 void frame_vector_to_pfns(struct frame_vector *vec)
 177 {
 178         int i;
 179         unsigned long *nums;
 180         struct page **pages;
 181
 182         if (vec->is_pfns)
 183                 return;
 184         pages = (struct page **)(vec->ptrs);
 185         nums = (unsigned long *)pages;
 186         for (i = 0; i < vec->nr_frames; i++)
 187                 nums[i] = page_to_pfn(pages[i]);
 188         vec->is_pfns = true;
 189 }
 190 EXPORT_SYMBOL(frame_vector_to_pfns);
 191
 192 /**
 193  * frame_vector_create() - allocate & initialize structure for pinned pfns
 194  * @nr_frames:  number of pfns slots we should reserve
 195  *
 196  * Allocate and initialize struct pinned_pfns to be able to hold @nr_pfns
 197  * pfns.
 198  */
 199 struct frame_vector *frame_vector_create(unsigned int nr_frames)
 200 {
 201         struct frame_vector *vec;
 202         int size = sizeof(struct frame_vector) + sizeof(void *) * nr_frames;
 203
 204         if (WARN_ON_ONCE(nr_frames == 0))
 205                 return NULL;
 206         /*
 207          * This is absurdly high. It's here just to avoid strange effects when
 208          * arithmetics overflows.
 209          */
 210         if (WARN_ON_ONCE(nr_frames > INT_MAX / sizeof(void *) / 2))
 211                 return NULL;
 212         /*
 213          * Avoid higher order allocations, use vmalloc instead. It should
 214          * be rare anyway.
 215          */
 216         vec = kvmalloc(size, GFP_KERNEL);
 217         if (!vec)
 218                 return NULL;
 219         vec->nr_allocated = nr_frames;
 220         vec->nr_frames = 0;
 221         return vec;
 222 }
 223 EXPORT_SYMBOL(frame_vector_create);
 224
 225 /**
 226  * frame_vector_destroy() - free memory allocated to carry frame vector
 227  * @vec:        Frame vector to free
 228  *
 229  * Free structure allocated by frame_vector_create() to carry frames.
 230  */
 231 void frame_vector_destroy(struct frame_vector *vec)
 232 {
 233         /* Make sure put_vaddr_frames() got called properly... */
 234         VM_BUG_ON(vec->nr_frames > 0);
 235         kvfree(vec);
 236 }
 237 EXPORT_SYMBOL(frame_vector_destroy);