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                  * Similar to the PMD case, NUMA hinting must take slow path
  41                  */
  42                 if (pte_numa(pte))
  43                         return 0;
  44
  45                 if ((pte_val(pte) & mask) != result)
  46                         return 0;
  47                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  48                 page = pte_page(pte);
  49                 if (!page_cache_get_speculative(page))
  50                         return 0;
  51                 if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  52                         put_page(page);
  53                         return 0;
  54                 }
  55                 pages[*nr] = page;
  56                 (*nr)++;
  57
  58         } while (ptep++, addr += PAGE_SIZE, addr != end);
  59
  60         return 1;
  61 }
  62
  63 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
  64                 int write, struct page **pages, int *nr)
  65 {
  66         unsigned long next;
  67         pmd_t *pmdp;
  68
  69         pmdp = pmd_offset(&pud, addr);
  70         do {
  71                 pmd_t pmd = ACCESS_ONCE(*pmdp);
  72
  73                 next = pmd_addr_end(addr, end);
  74                 /*
  75                  * If we find a splitting transparent hugepage we
  76                  * return zero. That will result in taking the slow
  77                  * path which will call wait_split_huge_page()
  78                  * if the pmd is still in splitting state
  79                  */
  80                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
  81                         return 0;
  82                 if (pmd_huge(pmd) || pmd_large(pmd)) {
  83                         /*
  84                          * NUMA hinting faults need to be handled in the GUP
  85                          * slowpath for accounting purposes and so that they
  86                          * can be serialised against THP migration.
  87                          */
  88                         if (pmd_numa(pmd))
  89                                 return 0;
  90
  91                         if (!gup_hugepte((pte_t *)pmdp, PMD_SIZE, addr, next,
  92                                          write, pages, nr))
  93                                 return 0;
  94                 } else if (is_hugepd(pmdp)) {
  95                         if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
  96                                         addr, next, write, pages, nr))
  97                                 return 0;
  98                 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
  99                         return 0;
 100         } while (pmdp++, addr = next, addr != end);
 101
 102         return 1;
 103 }
 104
 105 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 106                 int write, struct page **pages, int *nr)
 107 {
 108         unsigned long next;
 109         pud_t *pudp;
 110
 111         pudp = pud_offset(&pgd, addr);
 112         do {
 113                 pud_t pud = ACCESS_ONCE(*pudp);
 114
 115                 next = pud_addr_end(addr, end);
 116                 if (pud_none(pud))
 117                         return 0;
 118                 if (pud_huge(pud)) {
 119                         if (!gup_hugepte((pte_t *)pudp, PUD_SIZE, addr, next,
 120                                          write, pages, nr))
 121                                 return 0;
 122                 } else if (is_hugepd(pudp)) {
 123                         if (!gup_hugepd((hugepd_t *)pudp, PUD_SHIFT,
 124                                         addr, next, write, pages, nr))
 125                                 return 0;
 126                 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 127                         return 0;
 128         } while (pudp++, addr = next, addr != end);
 129
 130         return 1;
 131 }
 132
 133 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 134                           struct page **pages)
 135 {
 136         struct mm_struct *mm = current->mm;
 137         unsigned long addr, len, end;
 138         unsigned long next;
 139         unsigned long flags;
 140         pgd_t *pgdp;
 141         int nr = 0;
 142
 143         pr_devel("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
 144
 145         start &= PAGE_MASK;
 146         addr = start;
 147         len = (unsigned long) nr_pages << PAGE_SHIFT;
 148         end = start + len;
 149
 150         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 151                                         start, len)))
 152                 return 0;
 153
 154         pr_devel("  aligned: %lx .. %lx\n", start, end);
 155
 156         /*
 157          * XXX: batch / limit 'nr', to avoid large irq off latency
 158          * needs some instrumenting to determine the common sizes used by
 159          * important workloads (eg. DB2), and whether limiting the batch size
 160          * will decrease performance.
 161          *
 162          * It seems like we're in the clear for the moment. Direct-IO is
 163          * the main guy that batches up lots of get_user_pages, and even
 164          * they are limited to 64-at-a-time which is not so many.
 165          */
 166         /*
 167          * This doesn't prevent pagetable teardown, but does prevent
 168          * the pagetables from being freed on powerpc.
 169          *
 170          * So long as we atomically load page table pointers versus teardown,
 171          * we can follow the address down to the the page and take a ref on it.
 172          */
 173         local_irq_save(flags);
 174
 175         pgdp = pgd_offset(mm, addr);
 176         do {
 177                 pgd_t pgd = ACCESS_ONCE(*pgdp);
 178
 179                 pr_devel("  %016lx: normal pgd %p\n", addr,
 180                          (void *)pgd_val(pgd));
 181                 next = pgd_addr_end(addr, end);
 182                 if (pgd_none(pgd))
 183                         break;
 184                 if (pgd_huge(pgd)) {
 185                         if (!gup_hugepte((pte_t *)pgdp, PGDIR_SIZE, addr, next,
 186                                          write, pages, &nr))
 187                                 break;
 188                 } else if (is_hugepd(pgdp)) {
 189                         if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,
 190                                         addr, next, write, pages, &nr))
 191                                 break;
 192                 } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 193                         break;
 194         } while (pgdp++, addr = next, addr != end);
 195
 196         local_irq_restore(flags);
 197
 198         return nr;
 199 }
 200
 201 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 202                         struct page **pages)
 203 {
 204         struct mm_struct *mm = current->mm;
 205         int nr, ret;
 206
 207         start &= PAGE_MASK;
 208         nr = __get_user_pages_fast(start, nr_pages, write, pages);
 209         ret = nr;
 210
 211         if (nr < nr_pages) {
 212                 pr_devel("  slow path ! nr = %d\n", nr);
 213
 214                 /* Try to get the remaining pages with get_user_pages */
 215                 start += nr << PAGE_SHIFT;
 216                 pages += nr;
 217
 218                 down_read(&mm->mmap_sem);
 219                 ret = get_user_pages(current, mm, start,
 220                                      nr_pages - nr, write, 0, pages, NULL);
 221                 up_read(&mm->mmap_sem);
 222
 223                 /* Have to be a bit careful with return values */
 224                 if (nr > 0) {
 225                         if (ret < 0)
 226                                 ret = nr;
 227                         else
 228                                 ret += nr;
 229                 }
 230         }
 231
 232         return ret;
 233 }
 234
 235 #endif /* __HAVE_ARCH_PTE_SPECIAL */