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