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 #ifdef CONFIG_HUGETLB_PAGE
  59 static noinline int gup_huge_pte(pte_t *ptep, struct hstate *hstate,
  60                                  unsigned long *addr, unsigned long end,
  61                                  int write, struct page **pages, int *nr)
  62 {
  63         unsigned long mask;
  64         unsigned long pte_end;
  65         struct page *head, *page;
  66         pte_t pte;
  67         int refs;
  68
  69         pte_end = (*addr + huge_page_size(hstate)) & huge_page_mask(hstate);
  70         if (pte_end < end)
  71                 end = pte_end;
  72
  73         pte = *ptep;
  74         mask = _PAGE_PRESENT|_PAGE_USER;
  75         if (write)
  76                 mask |= _PAGE_RW;
  77         if ((pte_val(pte) & mask) != mask)
  78                 return 0;
  79         /* hugepages are never "special" */
  80         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  81
  82         refs = 0;
  83         head = pte_page(pte);
  84         page = head + ((*addr & ~huge_page_mask(hstate)) >> PAGE_SHIFT);
  85         do {
  86                 VM_BUG_ON(compound_head(page) != head);
  87                 pages[*nr] = page;
  88                 (*nr)++;
  89                 page++;
  90                 refs++;
  91         } while (*addr += PAGE_SIZE, *addr != end);
  92
  93         if (!page_cache_add_speculative(head, refs)) {
  94                 *nr -= refs;
  95                 return 0;
  96         }
  97         if (unlikely(pte_val(pte) != pte_val(*ptep))) {
  98                 /* Could be optimized better */
  99                 while (*nr) {
 100                         put_page(page);
 101                         (*nr)--;
 102                 }
 103         }
 104
 105         return 1;
 106 }
 107 #endif /* CONFIG_HUGETLB_PAGE */
 108
 109 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 110                 int write, struct page **pages, int *nr)
 111 {
 112         unsigned long next;
 113         pmd_t *pmdp;
 114
 115         pmdp = pmd_offset(&pud, addr);
 116         do {
 117                 pmd_t pmd = *pmdp;
 118
 119                 next = pmd_addr_end(addr, end);
 120                 if (pmd_none(pmd))
 121                         return 0;
 122                 if (!gup_pte_range(pmd, addr, next, write, pages, nr))
 123                         return 0;
 124         } while (pmdp++, addr = next, addr != end);
 125
 126         return 1;
 127 }
 128
 129 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 130                 int write, struct page **pages, int *nr)
 131 {
 132         unsigned long next;
 133         pud_t *pudp;
 134
 135         pudp = pud_offset(&pgd, addr);
 136         do {
 137                 pud_t pud = *pudp;
 138
 139                 next = pud_addr_end(addr, end);
 140                 if (pud_none(pud))
 141                         return 0;
 142                 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 143                         return 0;
 144         } while (pudp++, addr = next, addr != end);
 145
 146         return 1;
 147 }
 148
 149 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 150                         struct page **pages)
 151 {
 152         struct mm_struct *mm = current->mm;
 153         unsigned long addr, len, end;
 154         unsigned long next;
 155         pgd_t *pgdp;
 156         int nr = 0;
 157 #ifdef CONFIG_PPC64
 158         unsigned int shift;
 159         int psize;
 160 #endif
 161
 162         pr_debug("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
 163
 164         start &= PAGE_MASK;
 165         addr = start;
 166         len = (unsigned long) nr_pages << PAGE_SHIFT;
 167         end = start + len;
 168
 169         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 170                                         start, len)))
 171                 goto slow_irqon;
 172
 173         pr_debug("  aligned: %lx .. %lx\n", start, end);
 174
 175 #ifdef CONFIG_HUGETLB_PAGE
 176         /* We bail out on slice boundary crossing when hugetlb is
 177          * enabled in order to not have to deal with two different
 178          * page table formats
 179          */
 180         if (addr < SLICE_LOW_TOP) {
 181                 if (end > SLICE_LOW_TOP)
 182                         goto slow_irqon;
 183
 184                 if (unlikely(GET_LOW_SLICE_INDEX(addr) !=
 185                              GET_LOW_SLICE_INDEX(end - 1)))
 186                         goto slow_irqon;
 187         } else {
 188                 if (unlikely(GET_HIGH_SLICE_INDEX(addr) !=
 189                              GET_HIGH_SLICE_INDEX(end - 1)))
 190                         goto slow_irqon;
 191         }
 192 #endif /* CONFIG_HUGETLB_PAGE */
 193
 194         /*
 195          * XXX: batch / limit 'nr', to avoid large irq off latency
 196          * needs some instrumenting to determine the common sizes used by
 197          * important workloads (eg. DB2), and whether limiting the batch size
 198          * will decrease performance.
 199          *
 200          * It seems like we're in the clear for the moment. Direct-IO is
 201          * the main guy that batches up lots of get_user_pages, and even
 202          * they are limited to 64-at-a-time which is not so many.
 203          */
 204         /*
 205          * This doesn't prevent pagetable teardown, but does prevent
 206          * the pagetables from being freed on powerpc.
 207          *
 208          * So long as we atomically load page table pointers versus teardown,
 209          * we can follow the address down to the the page and take a ref on it.
 210          */
 211         local_irq_disable();
 212
 213 #ifdef CONFIG_PPC64
 214         /* Those bits are related to hugetlbfs implementation and only exist
 215          * on 64-bit for now
 216          */
 217         psize = get_slice_psize(mm, addr);
 218         shift = mmu_psize_defs[psize].shift;
 219 #endif /* CONFIG_PPC64 */
 220
 221 #ifdef CONFIG_HUGETLB_PAGE
 222         if (unlikely(mmu_huge_psizes[psize])) {
 223                 pte_t *ptep;
 224                 unsigned long a = addr;
 225                 unsigned long sz = ((1UL) << shift);
 226                 struct hstate *hstate = size_to_hstate(sz);
 227
 228                 BUG_ON(!hstate);
 229                 /*
 230                  * XXX: could be optimized to avoid hstate
 231                  * lookup entirely (just use shift)
 232                  */
 233
 234                 do {
 235                         VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, a)].shift);
 236                         ptep = huge_pte_offset(mm, a);
 237                         pr_debug(" %016lx: huge ptep %p\n", a, ptep);
 238                         if (!ptep || !gup_huge_pte(ptep, hstate, &a, end, write, pages,
 239                                                    &nr))
 240                                 goto slow;
 241                 } while (a != end);
 242         } else
 243 #endif /* CONFIG_HUGETLB_PAGE */
 244         {
 245                 pgdp = pgd_offset(mm, addr);
 246                 do {
 247                         pgd_t pgd = *pgdp;
 248
 249 #ifdef CONFIG_PPC64
 250                         VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, addr)].shift);
 251 #endif
 252                         pr_debug("  %016lx: normal pgd %p\n", addr,
 253                                  (void *)pgd_val(pgd));
 254                         next = pgd_addr_end(addr, end);
 255                         if (pgd_none(pgd))
 256                                 goto slow;
 257                         if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 258                                 goto slow;
 259                 } while (pgdp++, addr = next, addr != end);
 260         }
 261         local_irq_enable();
 262
 263         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 264         return nr;
 265
 266         {
 267                 int ret;
 268
 269 slow:
 270                 local_irq_enable();
 271 slow_irqon:
 272                 pr_debug("  slow path ! nr = %d\n", nr);
 273
 274                 /* Try to get the remaining pages with get_user_pages */
 275                 start += nr << PAGE_SHIFT;
 276                 pages += nr;
 277
 278                 down_read(&mm->mmap_sem);
 279                 ret = get_user_pages(current, mm, start,
 280                         (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
 281                 up_read(&mm->mmap_sem);
 282
 283                 /* Have to be a bit careful with return values */
 284                 if (nr > 0) {
 285                         if (ret < 0)
 286                                 ret = nr;
 287                         else
 288                                 ret += nr;
 289                 }
 290
 291                 return ret;
 292         }
 293 }
 294
 295 #endif /* __HAVE_ARCH_PTE_SPECIAL */