arch/powerpc/mm/gup.c

   1 /*
   2  * Lockless get_user_pages_fast for powerpc
   3  *
   4  * Copyright (C) 2008 Nick Piggin
   5  * Copyright (C) 2008 Novell Inc.
   6  */
   7 #undef DEBUG
   8
   9 #include <linux/sched.h>
  10 #include <linux/mm.h>
  11 #include <linux/hugetlb.h>
  12 #include <linux/vmstat.h>
  13 #include <linux/pagemap.h>
  14 #include <linux/rwsem.h>
  15 #include <asm/pgtable.h>
  16
  17 #ifdef __HAVE_ARCH_PTE_SPECIAL
  18
  19 /*
  20  * The performance critical leaf functions are made noinline otherwise gcc
  21  * inlines everything into a single function which results in too much
  22  * register pressure.
  23  */
  24 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
  25                 unsigned long end, int write, struct page **pages, int *nr)
  26 {
  27         unsigned long mask, result;
  28         pte_t *ptep;
  29
  30         result = _PAGE_PRESENT|_PAGE_USER;
  31         if (write)
  32                 result |= _PAGE_RW;
  33         mask = result | _PAGE_SPECIAL;
  34
  35         ptep = pte_offset_kernel(&pmd, addr);
  36         do {
  37                 pte_t pte = ACCESS_ONCE(*ptep);
  38                 struct page *page;
  39
  40                 if ((pte_val(pte) & mask) != result)
  41                         return 0;
  42                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  43                 page = pte_page(pte);
  44                 if (!page_cache_get_speculative(page))
  45                         return 0;
  46                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  47                         put_page(page);
  48                         return 0;
  49                 }
  50                 pages[*nr] = page;
  51                 (*nr)++;
  52
  53         } while (ptep++, addr += PAGE_SIZE, addr != end);
  54
  55         return 1;
  56 }
  57
  58 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
  59                 int write, struct page **pages, int *nr)
  60 {
  61         unsigned long next;
  62         pmd_t *pmdp;
  63
  64         pmdp = pmd_offset(&pud, addr);
  65         do {
  66                 pmd_t pmd = ACCESS_ONCE(*pmdp);
  67
  68                 next = pmd_addr_end(addr, end);
  69                 /*
  70                  * If we find a splitting transparent hugepage we
  71                  * return zero. That will result in taking the slow
  72                  * path which will call wait_split_huge_page()
  73                  * if the pmd is still in splitting state
  74                  */
  75                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
  76                         return 0;
  77                 if (pmd_huge(pmd) || pmd_large(pmd)) {
  78                         if (!gup_hugepte((pte_t *)pmdp, PMD_SIZE, addr, next,
  79                                          write, pages, nr))
  80                                 return 0;
  81                 } else if (is_hugepd(pmdp)) {
  82                         if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
  83                                         addr, next, write, pages, nr))
  84                                 return 0;
  85                 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
  86                         return 0;
  87         } while (pmdp++, addr = next, addr != end);
  88
  89         return 1;
  90 }
  91
  92 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
  93                 int write, struct page **pages, int *nr)
  94 {
  95         unsigned long next;
  96         pud_t *pudp;
  97
  98         pudp = pud_offset(&pgd, addr);
  99         do {
 100                 pud_t pud = ACCESS_ONCE(*pudp);
 101
 102                 next = pud_addr_end(addr, end);
 103                 if (pud_none(pud))
 104                         return 0;
 105                 if (pud_huge(pud)) {
 106                         if (!gup_hugepte((pte_t *)pudp, PUD_SIZE, addr, next,
 107                                          write, pages, nr))
 108                                 return 0;
 109                 } else if (is_hugepd(pudp)) {
 110                         if (!gup_hugepd((hugepd_t *)pudp, PUD_SHIFT,
 111                                         addr, next, write, pages, nr))
 112                                 return 0;
 113                 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 114                         return 0;
 115         } while (pudp++, addr = next, addr != end);
 116
 117         return 1;
 118 }
 119
 120 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 121                           struct page **pages)
 122 {
 123         struct mm_struct *mm = current->mm;
 124         unsigned long addr, len, end;
 125         unsigned long next;
 126         unsigned long flags;
 127         pgd_t *pgdp;
 128         int nr = 0;
 129
 130         pr_devel("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
 131
 132         start &= PAGE_MASK;
 133         addr = start;
 134         len = (unsigned long) nr_pages << PAGE_SHIFT;
 135         end = start + len;
 136
 137         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 138                                         start, len)))
 139                 return 0;
 140
 141         pr_devel("  aligned: %lx .. %lx\n", start, end);
 142
 143         /*
 144          * XXX: batch / limit 'nr', to avoid large irq off latency
 145          * needs some instrumenting to determine the common sizes used by
 146          * important workloads (eg. DB2), and whether limiting the batch size
 147          * will decrease performance.
 148          *
 149          * It seems like we're in the clear for the moment. Direct-IO is
 150          * the main guy that batches up lots of get_user_pages, and even
 151          * they are limited to 64-at-a-time which is not so many.
 152          */
 153         /*
 154          * This doesn't prevent pagetable teardown, but does prevent
 155          * the pagetables from being freed on powerpc.
 156          *
 157          * So long as we atomically load page table pointers versus teardown,
 158          * we can follow the address down to the the page and take a ref on it.
 159          */
 160         local_irq_save(flags);
 161
 162         pgdp = pgd_offset(mm, addr);
 163         do {
 164                 pgd_t pgd = ACCESS_ONCE(*pgdp);
 165
 166                 pr_devel("  %016lx: normal pgd %p\n", addr,
 167                          (void *)pgd_val(pgd));
 168                 next = pgd_addr_end(addr, end);
 169                 if (pgd_none(pgd))
 170                         break;
 171                 if (pgd_huge(pgd)) {
 172                         if (!gup_hugepte((pte_t *)pgdp, PGDIR_SIZE, addr, next,
 173                                          write, pages, &nr))
 174                                 break;
 175                 } else if (is_hugepd(pgdp)) {
 176                         if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,
 177                                         addr, next, write, pages, &nr))
 178                                 break;
 179                 } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 180                         break;
 181         } while (pgdp++, addr = next, addr != end);
 182
 183         local_irq_restore(flags);
 184
 185         return nr;
 186 }
 187
 188 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 189                         struct page **pages)
 190 {
 191         struct mm_struct *mm = current->mm;
 192         int nr, ret;
 193
 194         start &= PAGE_MASK;
 195         nr = __get_user_pages_fast(start, nr_pages, write, pages);
 196         ret = nr;
 197
 198         if (nr < nr_pages) {
 199                 pr_devel("  slow path ! nr = %d\n", nr);
 200
 201                 /* Try to get the remaining pages with get_user_pages */
 202                 start += nr << PAGE_SHIFT;
 203                 pages += nr;
 204
 205                 down_read(&mm->mmap_sem);
 206                 ret = get_user_pages(current, mm, start,
 207                                      nr_pages - nr, write, 0, pages, NULL);
 208                 up_read(&mm->mmap_sem);
 209
 210                 /* Have to be a bit careful with return values */
 211                 if (nr > 0) {
 212                         if (ret < 0)
 213                                 ret = nr;
 214                         else
 215                                 ret += nr;
 216                 }
 217         }
 218
 219         return ret;
 220 }
 221
 222 #endif /* __HAVE_ARCH_PTE_SPECIAL */