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 /*
  18  * The performance critical leaf functions are made noinline otherwise gcc
  19  * inlines everything into a single function which results in too much
  20  * register pressure.
  21  */
  22 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
  23                 unsigned long end, int write, struct page **pages, int *nr)
  24 {
  25         unsigned long mask, result;
  26         pte_t *ptep;
  27
  28         result = _PAGE_PRESENT|_PAGE_USER;
  29         if (write)
  30                 result |= _PAGE_RW;
  31         mask = result | _PAGE_SPECIAL;
  32
  33         ptep = pte_offset_kernel(&pmd, addr);
  34         do {
  35                 pte_t pte = *ptep;
  36                 struct page *page;
  37
  38                 if ((pte_val(pte) & mask) != result)
  39                         return 0;
  40                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  41                 page = pte_page(pte);
  42                 if (!page_cache_get_speculative(page))
  43                         return 0;
  44                 if (unlikely(pte != *ptep)) {
  45                         put_page(page);
  46                         return 0;
  47                 }
  48                 pages[*nr] = page;
  49                 (*nr)++;
  50
  51         } while (ptep++, addr += PAGE_SIZE, addr != end);
  52
  53         return 1;
  54 }
  55
  56 #ifdef CONFIG_HUGETLB_PAGE
  57 static noinline int gup_huge_pte(pte_t *ptep, struct hstate *hstate,
  58                                  unsigned long *addr, unsigned long end,
  59                                  int write, struct page **pages, int *nr)
  60 {
  61         unsigned long mask;
  62         unsigned long pte_end;
  63         struct page *head, *page;
  64         pte_t pte;
  65         int refs;
  66
  67         pte_end = (*addr + huge_page_size(hstate)) & huge_page_mask(hstate);
  68         if (pte_end < end)
  69                 end = pte_end;
  70
  71         pte = *ptep;
  72         mask = _PAGE_PRESENT|_PAGE_USER;
  73         if (write)
  74                 mask |= _PAGE_RW;
  75         if ((pte_val(pte) & mask) != mask)
  76                 return 0;
  77         /* hugepages are never "special" */
  78         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  79
  80         refs = 0;
  81         head = pte_page(pte);
  82         page = head + ((*addr & ~huge_page_mask(hstate)) >> PAGE_SHIFT);
  83         do {
  84                 VM_BUG_ON(compound_head(page) != head);
  85                 pages[*nr] = page;
  86                 (*nr)++;
  87                 page++;
  88                 refs++;
  89         } while (*addr += PAGE_SIZE, *addr != end);
  90
  91         if (!page_cache_add_speculative(head, refs)) {
  92                 *nr -= refs;
  93                 return 0;
  94         }
  95         if (unlikely(pte != *ptep)) {
  96                 /* Could be optimized better */
  97                 while (*nr) {
  98                         put_page(page);
  99                         (*nr)--;
 100                 }
 101         }
 102
 103         return 1;
 104 }
 105 #endif /* CONFIG_HUGETLB_PAGE */
 106
 107 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 108                 int write, struct page **pages, int *nr)
 109 {
 110         unsigned long next;
 111         pmd_t *pmdp;
 112
 113         pmdp = pmd_offset(&pud, addr);
 114         do {
 115                 pmd_t pmd = *pmdp;
 116
 117                 next = pmd_addr_end(addr, end);
 118                 if (pmd_none(pmd))
 119                         return 0;
 120                 if (!gup_pte_range(pmd, addr, next, write, pages, nr))
 121                         return 0;
 122         } while (pmdp++, addr = next, addr != end);
 123
 124         return 1;
 125 }
 126
 127 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 128                 int write, struct page **pages, int *nr)
 129 {
 130         unsigned long next;
 131         pud_t *pudp;
 132
 133         pudp = pud_offset(&pgd, addr);
 134         do {
 135                 pud_t pud = *pudp;
 136
 137                 next = pud_addr_end(addr, end);
 138                 if (pud_none(pud))
 139                         return 0;
 140                 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 141                         return 0;
 142         } while (pudp++, addr = next, addr != end);
 143
 144         return 1;
 145 }
 146
 147 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 148                         struct page **pages)
 149 {
 150         struct mm_struct *mm = current->mm;
 151         unsigned long addr, len, end;
 152         unsigned long next;
 153         pgd_t *pgdp;
 154         int psize, nr = 0;
 155         unsigned int shift;
 156
 157         pr_debug("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
 158
 159         start &= PAGE_MASK;
 160         addr = start;
 161         len = (unsigned long) nr_pages << PAGE_SHIFT;
 162         end = start + len;
 163
 164         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 165                                         start, len)))
 166                 goto slow_irqon;
 167
 168         pr_debug("  aligned: %lx .. %lx\n", start, end);
 169
 170 #ifdef CONFIG_HUGETLB_PAGE
 171         /* We bail out on slice boundary crossing when hugetlb is
 172          * enabled in order to not have to deal with two different
 173          * page table formats
 174          */
 175         if (addr < SLICE_LOW_TOP) {
 176                 if (end > SLICE_LOW_TOP)
 177                         goto slow_irqon;
 178
 179                 if (unlikely(GET_LOW_SLICE_INDEX(addr) !=
 180                              GET_LOW_SLICE_INDEX(end - 1)))
 181                         goto slow_irqon;
 182         } else {
 183                 if (unlikely(GET_HIGH_SLICE_INDEX(addr) !=
 184                              GET_HIGH_SLICE_INDEX(end - 1)))
 185                         goto slow_irqon;
 186         }
 187 #endif /* CONFIG_HUGETLB_PAGE */
 188
 189         /*
 190          * XXX: batch / limit 'nr', to avoid large irq off latency
 191          * needs some instrumenting to determine the common sizes used by
 192          * important workloads (eg. DB2), and whether limiting the batch size
 193          * will decrease performance.
 194          *
 195          * It seems like we're in the clear for the moment. Direct-IO is
 196          * the main guy that batches up lots of get_user_pages, and even
 197          * they are limited to 64-at-a-time which is not so many.
 198          */
 199         /*
 200          * This doesn't prevent pagetable teardown, but does prevent
 201          * the pagetables from being freed on powerpc.
 202          *
 203          * So long as we atomically load page table pointers versus teardown,
 204          * we can follow the address down to the the page and take a ref on it.
 205          */
 206         local_irq_disable();
 207
 208         psize = get_slice_psize(mm, addr);
 209         shift = mmu_psize_defs[psize].shift;
 210
 211 #ifdef CONFIG_HUGETLB_PAGE
 212         if (unlikely(mmu_huge_psizes[psize])) {
 213                 pte_t *ptep;
 214                 unsigned long a = addr;
 215                 unsigned long sz = ((1UL) << shift);
 216                 struct hstate *hstate = size_to_hstate(sz);
 217
 218                 BUG_ON(!hstate);
 219                 /*
 220                  * XXX: could be optimized to avoid hstate
 221                  * lookup entirely (just use shift)
 222                  */
 223
 224                 do {
 225                         VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, a)].shift);
 226                         ptep = huge_pte_offset(mm, a);
 227                         pr_debug(" %016lx: huge ptep %p\n", a, ptep);
 228                         if (!ptep || !gup_huge_pte(ptep, hstate, &a, end, write, pages,
 229                                                    &nr))
 230                                 goto slow;
 231                 } while (a != end);
 232         } else
 233 #endif /* CONFIG_HUGETLB_PAGE */
 234         {
 235                 pgdp = pgd_offset(mm, addr);
 236                 do {
 237                         pgd_t pgd = *pgdp;
 238
 239                         VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, addr)].shift);
 240                         pr_debug("  %016lx: normal pgd %p\n", addr, (void *)pgd);
 241                         next = pgd_addr_end(addr, end);
 242                         if (pgd_none(pgd))
 243                                 goto slow;
 244                         if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 245                                 goto slow;
 246                 } while (pgdp++, addr = next, addr != end);
 247         }
 248         local_irq_enable();
 249
 250         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 251         return nr;
 252
 253         {
 254                 int ret;
 255
 256 slow:
 257                 local_irq_enable();
 258 slow_irqon:
 259                 pr_debug("  slow path ! nr = %d\n", nr);
 260
 261                 /* Try to get the remaining pages with get_user_pages */
 262                 start += nr << PAGE_SHIFT;
 263                 pages += nr;
 264
 265                 down_read(&mm->mmap_sem);
 266                 ret = get_user_pages(current, mm, start,
 267                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
 268                 up_read(&mm->mmap_sem);
 269
 270                 /* Have to be a bit careful with return values */
 271                 if (nr > 0) {
 272                         if (ret < 0)
 273                                 ret = nr;
 274                         else
 275                                 ret += nr;
 276                 }
 277
 278                 return ret;
 279         }
 280 }