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 = *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 = *pmdp;
  67
  68                 next = pmd_addr_end(addr, end);
  69                 if (pmd_none(pmd))
  70                         return 0;
  71                 if (is_hugepd(pmdp)) {
  72                         if (!gup_hugepd((hugepd_t *)pmdp, PMD_SHIFT,
  73                                         addr, next, write, pages, nr))
  74                                 return 0;
  75                 } else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
  76                         return 0;
  77         } while (pmdp++, addr = next, addr != end);
  78
  79         return 1;
  80 }
  81
  82 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
  83                 int write, struct page **pages, int *nr)
  84 {
  85         unsigned long next;
  86         pud_t *pudp;
  87
  88         pudp = pud_offset(&pgd, addr);
  89         do {
  90                 pud_t pud = *pudp;
  91
  92                 next = pud_addr_end(addr, end);
  93                 if (pud_none(pud))
  94                         return 0;
  95                 if (is_hugepd(pudp)) {
  96                         if (!gup_hugepd((hugepd_t *)pudp, PUD_SHIFT,
  97                                         addr, next, write, pages, nr))
  98                                 return 0;
  99                 } else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 100                         return 0;
 101         } while (pudp++, addr = next, addr != end);
 102
 103         return 1;
 104 }
 105
 106 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 107                         struct page **pages)
 108 {
 109         struct mm_struct *mm = current->mm;
 110         unsigned long addr, len, end;
 111         unsigned long next;
 112         pgd_t *pgdp;
 113         int nr = 0;
 114
 115         pr_devel("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
 116
 117         start &= PAGE_MASK;
 118         addr = start;
 119         len = (unsigned long) nr_pages << PAGE_SHIFT;
 120         end = start + len;
 121
 122         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 123                                         start, len)))
 124                 goto slow_irqon;
 125
 126         pr_devel("  aligned: %lx .. %lx\n", start, end);
 127
 128         /*
 129          * XXX: batch / limit 'nr', to avoid large irq off latency
 130          * needs some instrumenting to determine the common sizes used by
 131          * important workloads (eg. DB2), and whether limiting the batch size
 132          * will decrease performance.
 133          *
 134          * It seems like we're in the clear for the moment. Direct-IO is
 135          * the main guy that batches up lots of get_user_pages, and even
 136          * they are limited to 64-at-a-time which is not so many.
 137          */
 138         /*
 139          * This doesn't prevent pagetable teardown, but does prevent
 140          * the pagetables from being freed on powerpc.
 141          *
 142          * So long as we atomically load page table pointers versus teardown,
 143          * we can follow the address down to the the page and take a ref on it.
 144          */
 145         local_irq_disable();
 146
 147         pgdp = pgd_offset(mm, addr);
 148         do {
 149                 pgd_t pgd = *pgdp;
 150
 151                 pr_devel("  %016lx: normal pgd %p\n", addr,
 152                          (void *)pgd_val(pgd));
 153                 next = pgd_addr_end(addr, end);
 154                 if (pgd_none(pgd))
 155                         goto slow;
 156                 if (is_hugepd(pgdp)) {
 157                         if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,
 158                                         addr, next, write, pages, &nr))
 159                                 goto slow;
 160                 } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 161                         goto slow;
 162         } while (pgdp++, addr = next, addr != end);
 163
 164         local_irq_enable();
 165
 166         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 167         return nr;
 168
 169         {
 170                 int ret;
 171
 172 slow:
 173                 local_irq_enable();
 174 slow_irqon:
 175                 pr_devel("  slow path ! nr = %d\n", nr);
 176
 177                 /* Try to get the remaining pages with get_user_pages */
 178                 start += nr << PAGE_SHIFT;
 179                 pages += nr;
 180
 181                 down_read(&mm->mmap_sem);
 182                 ret = get_user_pages(current, mm, start,
 183                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
 184                 up_read(&mm->mmap_sem);
 185
 186                 /* Have to be a bit careful with return values */
 187                 if (nr > 0) {
 188                         if (ret < 0)
 189                                 ret = nr;
 190                         else
 191                                 ret += nr;
 192                 }
 193
 194                 return ret;
 195         }
 196 }
 197
 198 #endif /* __HAVE_ARCH_PTE_SPECIAL */