arch/s390/mm/gup.c

   1 /*
   2  *  Lockless get_user_pages_fast for s390
   3  *
   4  *  Copyright IBM Corp. 2010
   5  *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
   6  */
   7 #include <linux/sched.h>
   8 #include <linux/mm.h>
   9 #include <linux/hugetlb.h>
  10 #include <linux/vmstat.h>
  11 #include <linux/pagemap.h>
  12 #include <linux/rwsem.h>
  13 #include <asm/pgtable.h>
  14
  15 /*
  16  * The performance critical leaf functions are made noinline otherwise gcc
  17  * inlines everything into a single function which results in too much
  18  * register pressure.
  19  */
  20 static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  21                 unsigned long end, int write, struct page **pages, int *nr)
  22 {
  23         unsigned long mask;
  24         pte_t *ptep, pte;
  25         struct page *page;
  26
  27         mask = (write ? _PAGE_PROTECT : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
  28
  29         ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
  30         do {
  31                 pte = *ptep;
  32                 barrier();
  33                 if ((pte_val(pte) & mask) != 0)
  34                         return 0;
  35                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  36                 page = pte_page(pte);
  37                 if (!page_cache_get_speculative(page))
  38                         return 0;
  39                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  40                         put_page(page);
  41                         return 0;
  42                 }
  43                 pages[*nr] = page;
  44                 (*nr)++;
  45
  46         } while (ptep++, addr += PAGE_SIZE, addr != end);
  47
  48         return 1;
  49 }
  50
  51 static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  52                 unsigned long end, int write, struct page **pages, int *nr)
  53 {
  54         unsigned long mask, result;
  55         struct page *head, *page, *tail;
  56         int refs;
  57
  58         result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
  59         mask = result | _SEGMENT_ENTRY_INVALID;
  60         if ((pmd_val(pmd) & mask) != result)
  61                 return 0;
  62         VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
  63
  64         refs = 0;
  65         head = pmd_page(pmd);
  66         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  67         tail = page;
  68         do {
  69                 VM_BUG_ON(compound_head(page) != head);
  70                 pages[*nr] = page;
  71                 (*nr)++;
  72                 page++;
  73                 refs++;
  74         } while (addr += PAGE_SIZE, addr != end);
  75
  76         if (!page_cache_add_speculative(head, refs)) {
  77                 *nr -= refs;
  78                 return 0;
  79         }
  80
  81         if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
  82                 *nr -= refs;
  83                 while (refs--)
  84                         put_page(head);
  85                 return 0;
  86         }
  87
  88         /*
  89          * Any tail page need their mapcount reference taken before we
  90          * return.
  91          */
  92         while (refs--) {
  93                 if (PageTail(tail))
  94                         get_huge_page_tail(tail);
  95                 tail++;
  96         }
  97
  98         return 1;
  99 }
 100
 101
 102 static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
 103                 unsigned long end, int write, struct page **pages, int *nr)
 104 {
 105         unsigned long next;
 106         pmd_t *pmdp, pmd;
 107
 108         pmdp = (pmd_t *) pudp;
 109 #ifdef CONFIG_64BIT
 110         if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
 111                 pmdp = (pmd_t *) pud_deref(pud);
 112         pmdp += pmd_index(addr);
 113 #endif
 114         do {
 115                 pmd = *pmdp;
 116                 barrier();
 117                 next = pmd_addr_end(addr, end);
 118                 /*
 119                  * The pmd_trans_splitting() check below explains why
 120                  * pmdp_splitting_flush() has to serialize with
 121                  * smp_call_function() against our disabled IRQs, to stop
 122                  * this gup-fast code from running while we set the
 123                  * splitting bit in the pmd. Returning zero will take
 124                  * the slow path that will call wait_split_huge_page()
 125                  * if the pmd is still in splitting state.
 126                  */
 127                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
 128                         return 0;
 129                 if (unlikely(pmd_large(pmd))) {
 130                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
 131                                           write, pages, nr))
 132                                 return 0;
 133                 } else if (!gup_pte_range(pmdp, pmd, addr, next,
 134                                           write, pages, nr))
 135                         return 0;
 136         } while (pmdp++, addr = next, addr != end);
 137
 138         return 1;
 139 }
 140
 141 static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
 142                 unsigned long end, int write, struct page **pages, int *nr)
 143 {
 144         unsigned long next;
 145         pud_t *pudp, pud;
 146
 147         pudp = (pud_t *) pgdp;
 148 #ifdef CONFIG_64BIT
 149         if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
 150                 pudp = (pud_t *) pgd_deref(pgd);
 151         pudp += pud_index(addr);
 152 #endif
 153         do {
 154                 pud = *pudp;
 155                 barrier();
 156                 next = pud_addr_end(addr, end);
 157                 if (pud_none(pud))
 158                         return 0;
 159                 if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
 160                         return 0;
 161         } while (pudp++, addr = next, addr != end);
 162
 163         return 1;
 164 }
 165
 166 /*
 167  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 168  * back to the regular GUP.
 169  */
 170 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 171                           struct page **pages)
 172 {
 173         struct mm_struct *mm = current->mm;
 174         unsigned long addr, len, end;
 175         unsigned long next, flags;
 176         pgd_t *pgdp, pgd;
 177         int nr = 0;
 178
 179         start &= PAGE_MASK;
 180         addr = start;
 181         len = (unsigned long) nr_pages << PAGE_SHIFT;
 182         end = start + len;
 183         if ((end <= start) || (end > TASK_SIZE))
 184                 return 0;
 185         /*
 186          * local_irq_save() doesn't prevent pagetable teardown, but does
 187          * prevent the pagetables from being freed on s390.
 188          *
 189          * So long as we atomically load page table pointers versus teardown,
 190          * we can follow the address down to the the page and take a ref on it.
 191          */
 192         local_irq_save(flags);
 193         pgdp = pgd_offset(mm, addr);
 194         do {
 195                 pgd = *pgdp;
 196                 barrier();
 197                 next = pgd_addr_end(addr, end);
 198                 if (pgd_none(pgd))
 199                         break;
 200                 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
 201                         break;
 202         } while (pgdp++, addr = next, addr != end);
 203         local_irq_restore(flags);
 204
 205         return nr;
 206 }
 207
 208 /**
 209  * get_user_pages_fast() - pin user pages in memory
 210  * @start:      starting user address
 211  * @nr_pages:   number of pages from start to pin
 212  * @write:      whether pages will be written to
 213  * @pages:      array that receives pointers to the pages pinned.
 214  *              Should be at least nr_pages long.
 215  *
 216  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 217  * If not successful, it will fall back to taking the lock and
 218  * calling get_user_pages().
 219  *
 220  * Returns number of pages pinned. This may be fewer than the number
 221  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 222  * were pinned, returns -errno.
 223  */
 224 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 225                         struct page **pages)
 226 {
 227         struct mm_struct *mm = current->mm;
 228         int nr, ret;
 229
 230         start &= PAGE_MASK;
 231         nr = __get_user_pages_fast(start, nr_pages, write, pages);
 232         if (nr == nr_pages)
 233                 return nr;
 234
 235         /* Try to get the remaining pages with get_user_pages */
 236         start += nr << PAGE_SHIFT;
 237         pages += nr;
 238         down_read(&mm->mmap_sem);
 239         ret = get_user_pages(current, mm, start,
 240                              nr_pages - nr, write, 0, pages, NULL);
 241         up_read(&mm->mmap_sem);
 242         /* Have to be a bit careful with return values */
 243         if (nr > 0)
 244                 ret = (ret < 0) ? nr : ret + nr;
 245         return ret;
 246 }