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                 /* Similar to the PMD case, NUMA hinting must take slow path */
  34                 if (pte_protnone(pte))
  35                         return 0;
  36                 if ((pte_val(pte) & mask) != 0)
  37                         return 0;
  38                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  39                 page = pte_page(pte);
  40                 if (!page_cache_get_speculative(page))
  41                         return 0;
  42                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  43                         put_page(page);
  44                         return 0;
  45                 }
  46                 pages[*nr] = page;
  47                 (*nr)++;
  48
  49         } while (ptep++, addr += PAGE_SIZE, addr != end);
  50
  51         return 1;
  52 }
  53
  54 static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
  55                 unsigned long end, int write, struct page **pages, int *nr)
  56 {
  57         unsigned long mask, result;
  58         struct page *head, *page, *tail;
  59         int refs;
  60
  61         result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
  62         mask = result | _SEGMENT_ENTRY_INVALID;
  63         if ((pmd_val(pmd) & mask) != result)
  64                 return 0;
  65         VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
  66
  67         refs = 0;
  68         head = pmd_page(pmd);
  69         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  70         tail = page;
  71         do {
  72                 VM_BUG_ON(compound_head(page) != head);
  73                 pages[*nr] = page;
  74                 (*nr)++;
  75                 page++;
  76                 refs++;
  77         } while (addr += PAGE_SIZE, addr != end);
  78
  79         if (!page_cache_add_speculative(head, refs)) {
  80                 *nr -= refs;
  81                 return 0;
  82         }
  83
  84         if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
  85                 *nr -= refs;
  86                 while (refs--)
  87                         put_page(head);
  88                 return 0;
  89         }
  90
  91         /*
  92          * Any tail page need their mapcount reference taken before we
  93          * return.
  94          */
  95         while (refs--) {
  96                 if (PageTail(tail))
  97                         get_huge_page_tail(tail);
  98                 tail++;
  99         }
 100
 101         return 1;
 102 }
 103
 104
 105 static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
 106                 unsigned long end, int write, struct page **pages, int *nr)
 107 {
 108         unsigned long next;
 109         pmd_t *pmdp, pmd;
 110
 111         pmdp = (pmd_t *) pudp;
 112         if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
 113                 pmdp = (pmd_t *) pud_deref(pud);
 114         pmdp += pmd_index(addr);
 115         do {
 116                 pmd = *pmdp;
 117                 barrier();
 118                 next = pmd_addr_end(addr, end);
 119                 /*
 120                  * The pmd_trans_splitting() check below explains why
 121                  * pmdp_splitting_flush() has to serialize with
 122                  * smp_call_function() against our disabled IRQs, to stop
 123                  * this gup-fast code from running while we set the
 124                  * splitting bit in the pmd. Returning zero will take
 125                  * the slow path that will call wait_split_huge_page()
 126                  * if the pmd is still in splitting state.
 127                  */
 128                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
 129                         return 0;
 130                 if (unlikely(pmd_large(pmd))) {
 131                         /*
 132                          * NUMA hinting faults need to be handled in the GUP
 133                          * slowpath for accounting purposes and so that they
 134                          * can be serialised against THP migration.
 135                          */
 136                         if (pmd_protnone(pmd))
 137                                 return 0;
 138                         if (!gup_huge_pmd(pmdp, pmd, addr, next,
 139                                           write, pages, nr))
 140                                 return 0;
 141                 } else if (!gup_pte_range(pmdp, pmd, addr, next,
 142                                           write, pages, nr))
 143                         return 0;
 144         } while (pmdp++, addr = next, addr != end);
 145
 146         return 1;
 147 }
 148
 149 static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
 150                 unsigned long end, int write, struct page **pages, int *nr)
 151 {
 152         unsigned long next;
 153         pud_t *pudp, pud;
 154
 155         pudp = (pud_t *) pgdp;
 156         if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
 157                 pudp = (pud_t *) pgd_deref(pgd);
 158         pudp += pud_index(addr);
 159         do {
 160                 pud = *pudp;
 161                 barrier();
 162                 next = pud_addr_end(addr, end);
 163                 if (pud_none(pud))
 164                         return 0;
 165                 if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
 166                         return 0;
 167         } while (pudp++, addr = next, addr != end);
 168
 169         return 1;
 170 }
 171
 172 /*
 173  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 174  * back to the regular GUP.
 175  */
 176 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 177                           struct page **pages)
 178 {
 179         struct mm_struct *mm = current->mm;
 180         unsigned long addr, len, end;
 181         unsigned long next, flags;
 182         pgd_t *pgdp, pgd;
 183         int nr = 0;
 184
 185         start &= PAGE_MASK;
 186         addr = start;
 187         len = (unsigned long) nr_pages << PAGE_SHIFT;
 188         end = start + len;
 189         if ((end <= start) || (end > TASK_SIZE))
 190                 return 0;
 191         /*
 192          * local_irq_save() doesn't prevent pagetable teardown, but does
 193          * prevent the pagetables from being freed on s390.
 194          *
 195          * So long as we atomically load page table pointers versus teardown,
 196          * we can follow the address down to the the page and take a ref on it.
 197          */
 198         local_irq_save(flags);
 199         pgdp = pgd_offset(mm, addr);
 200         do {
 201                 pgd = *pgdp;
 202                 barrier();
 203                 next = pgd_addr_end(addr, end);
 204                 if (pgd_none(pgd))
 205                         break;
 206                 if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
 207                         break;
 208         } while (pgdp++, addr = next, addr != end);
 209         local_irq_restore(flags);
 210
 211         return nr;
 212 }
 213
 214 /**
 215  * get_user_pages_fast() - pin user pages in memory
 216  * @start:      starting user address
 217  * @nr_pages:   number of pages from start to pin
 218  * @write:      whether pages will be written to
 219  * @pages:      array that receives pointers to the pages pinned.
 220  *              Should be at least nr_pages long.
 221  *
 222  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 223  * If not successful, it will fall back to taking the lock and
 224  * calling get_user_pages().
 225  *
 226  * Returns number of pages pinned. This may be fewer than the number
 227  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 228  * were pinned, returns -errno.
 229  */
 230 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 231                         struct page **pages)
 232 {
 233         struct mm_struct *mm = current->mm;
 234         int nr, ret;
 235
 236         start &= PAGE_MASK;
 237         nr = __get_user_pages_fast(start, nr_pages, write, pages);
 238         if (nr == nr_pages)
 239                 return nr;
 240
 241         /* Try to get the remaining pages with get_user_pages */
 242         start += nr << PAGE_SHIFT;
 243         pages += nr;
 244         ret = get_user_pages_unlocked(current, mm, start,
 245                              nr_pages - nr, write, 0, pages);
 246         /* Have to be a bit careful with return values */
 247         if (nr > 0)
 248                 ret = (ret < 0) ? nr : ret + nr;
 249         return ret;
 250 }