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