arch/mips/mm/gup.c

   1 /*
   2  * Lockless get_user_pages_fast for MIPS
   3  *
   4  * Copyright (C) 2008 Nick Piggin
   5  * Copyright (C) 2008 Novell Inc.
   6  * Copyright (C) 2011 Ralf Baechle
   7  */
   8 #include <linux/sched.h>
   9 #include <linux/mm.h>
  10 #include <linux/vmstat.h>
  11 #include <linux/highmem.h>
  12 #include <linux/swap.h>
  13 #include <linux/hugetlb.h>
  14
  15 #include <asm/pgtable.h>
  16
  17 static inline pte_t gup_get_pte(pte_t *ptep)
  18 {
  19 #if defined(CONFIG_64BIT_PHYS_ADDR) && defined(CONFIG_CPU_MIPS32)
  20         pte_t pte;
  21
  22 retry:
  23         pte.pte_low = ptep->pte_low;
  24         smp_rmb();
  25         pte.pte_high = ptep->pte_high;
  26         smp_rmb();
  27         if (unlikely(pte.pte_low != ptep->pte_low))
  28                 goto retry;
  29
  30         return pte;
  31 #else
  32         return ACCESS_ONCE(*ptep);
  33 #endif
  34 }
  35
  36 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
  37                         int write, struct page **pages, int *nr)
  38 {
  39         pte_t *ptep = pte_offset_map(&pmd, addr);
  40         do {
  41                 pte_t pte = gup_get_pte(ptep);
  42                 struct page *page;
  43
  44                 if (!pte_present(pte) ||
  45                     pte_special(pte) || (write && !pte_write(pte))) {
  46                         pte_unmap(ptep);
  47                         return 0;
  48                 }
  49                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  50                 page = pte_page(pte);
  51                 get_page(page);
  52                 SetPageReferenced(page);
  53                 pages[*nr] = page;
  54                 (*nr)++;
  55
  56         } while (ptep++, addr += PAGE_SIZE, addr != end);
  57
  58         pte_unmap(ptep - 1);
  59         return 1;
  60 }
  61
  62 static inline void get_head_page_multiple(struct page *page, int nr)
  63 {
  64         VM_BUG_ON(page != compound_head(page));
  65         VM_BUG_ON(page_count(page) == 0);
  66         atomic_add(nr, &page->_count);
  67         SetPageReferenced(page);
  68 }
  69
  70 static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
  71                         int write, struct page **pages, int *nr)
  72 {
  73         pte_t pte = *(pte_t *)&pmd;
  74         struct page *head, *page;
  75         int refs;
  76
  77         if (write && !pte_write(pte))
  78                 return 0;
  79         /* hugepages are never "special" */
  80         VM_BUG_ON(pte_special(pte));
  81         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  82
  83         refs = 0;
  84         head = pte_page(pte);
  85         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  86         do {
  87                 VM_BUG_ON(compound_head(page) != head);
  88                 pages[*nr] = page;
  89                 if (PageTail(page))
  90                         get_huge_page_tail(page);
  91                 (*nr)++;
  92                 page++;
  93                 refs++;
  94         } while (addr += PAGE_SIZE, addr != end);
  95
  96         get_head_page_multiple(head, refs);
  97         return 1;
  98 }
  99
 100 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 101                         int write, struct page **pages, int *nr)
 102 {
 103         unsigned long next;
 104         pmd_t *pmdp;
 105
 106         pmdp = pmd_offset(&pud, addr);
 107         do {
 108                 pmd_t pmd = *pmdp;
 109
 110                 next = pmd_addr_end(addr, end);
 111                 /*
 112                  * The pmd_trans_splitting() check below explains why
 113                  * pmdp_splitting_flush has to flush the tlb, to stop
 114                  * this gup-fast code from running while we set the
 115                  * splitting bit in the pmd. Returning zero will take
 116                  * the slow path that will call wait_split_huge_page()
 117                  * if the pmd is still in splitting state. gup-fast
 118                  * can't because it has irq disabled and
 119                  * wait_split_huge_page() would never return as the
 120                  * tlb flush IPI wouldn't run.
 121                  */
 122                 if (pmd_none(pmd) || pmd_trans_splitting(pmd))
 123                         return 0;
 124                 if (unlikely(pmd_huge(pmd))) {
 125                         if (!gup_huge_pmd(pmd, addr, next, write, pages,nr))
 126                                 return 0;
 127                 } else {
 128                         if (!gup_pte_range(pmd, addr, next, write, pages,nr))
 129                                 return 0;
 130                 }
 131         } while (pmdp++, addr = next, addr != end);
 132
 133         return 1;
 134 }
 135
 136 static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
 137                         int write, struct page **pages, int *nr)
 138 {
 139         pte_t pte = *(pte_t *)&pud;
 140         struct page *head, *page;
 141         int refs;
 142
 143         if (write && !pte_write(pte))
 144                 return 0;
 145         /* hugepages are never "special" */
 146         VM_BUG_ON(pte_special(pte));
 147         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 148
 149         refs = 0;
 150         head = pte_page(pte);
 151         page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 152         do {
 153                 VM_BUG_ON(compound_head(page) != head);
 154                 pages[*nr] = page;
 155                 (*nr)++;
 156                 page++;
 157                 refs++;
 158         } while (addr += PAGE_SIZE, addr != end);
 159
 160         get_head_page_multiple(head, refs);
 161         return 1;
 162 }
 163
 164 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 165                         int write, struct page **pages, int *nr)
 166 {
 167         unsigned long next;
 168         pud_t *pudp;
 169
 170         pudp = pud_offset(&pgd, addr);
 171         do {
 172                 pud_t pud = *pudp;
 173
 174                 next = pud_addr_end(addr, end);
 175                 if (pud_none(pud))
 176                         return 0;
 177                 if (unlikely(pud_huge(pud))) {
 178                         if (!gup_huge_pud(pud, addr, next, write, pages,nr))
 179                                 return 0;
 180                 } else {
 181                         if (!gup_pmd_range(pud, addr, next, write, pages,nr))
 182                                 return 0;
 183                 }
 184         } while (pudp++, addr = next, addr != end);
 185
 186         return 1;
 187 }
 188
 189 /*
 190  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 191  * back to the regular GUP.
 192  */
 193 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 194                           struct page **pages)
 195 {
 196         struct mm_struct *mm = current->mm;
 197         unsigned long addr, len, end;
 198         unsigned long next;
 199         unsigned long flags;
 200         pgd_t *pgdp;
 201         int nr = 0;
 202
 203         start &= PAGE_MASK;
 204         addr = start;
 205         len = (unsigned long) nr_pages << PAGE_SHIFT;
 206         end = start + len;
 207         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 208                                         (void __user *)start, len)))
 209                 return 0;
 210
 211         /*
 212          * XXX: batch / limit 'nr', to avoid large irq off latency
 213          * needs some instrumenting to determine the common sizes used by
 214          * important workloads (eg. DB2), and whether limiting the batch
 215          * size will decrease performance.
 216          *
 217          * It seems like we're in the clear for the moment. Direct-IO is
 218          * the main guy that batches up lots of get_user_pages, and even
 219          * they are limited to 64-at-a-time which is not so many.
 220          */
 221         /*
 222          * This doesn't prevent pagetable teardown, but does prevent
 223          * the pagetables and pages from being freed.
 224          *
 225          * So long as we atomically load page table pointers versus teardown,
 226          * we can follow the address down to the page and take a ref on it.
 227          */
 228         local_irq_save(flags);
 229         pgdp = pgd_offset(mm, addr);
 230         do {
 231                 pgd_t pgd = *pgdp;
 232
 233                 next = pgd_addr_end(addr, end);
 234                 if (pgd_none(pgd))
 235                         break;
 236                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 237                         break;
 238         } while (pgdp++, addr = next, addr != end);
 239         local_irq_restore(flags);
 240
 241         return nr;
 242 }
 243
 244 /**
 245  * get_user_pages_fast() - pin user pages in memory
 246  * @start:      starting user address
 247  * @nr_pages:   number of pages from start to pin
 248  * @write:      whether pages will be written to
 249  * @pages:      array that receives pointers to the pages pinned.
 250  *              Should be at least nr_pages long.
 251  *
 252  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 253  * If not successful, it will fall back to taking the lock and
 254  * calling get_user_pages().
 255  *
 256  * Returns number of pages pinned. This may be fewer than the number
 257  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 258  * were pinned, returns -errno.
 259  */
 260 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 261                         struct page **pages)
 262 {
 263         struct mm_struct *mm = current->mm;
 264         unsigned long addr, len, end;
 265         unsigned long next;
 266         pgd_t *pgdp;
 267         int ret, nr = 0;
 268
 269         start &= PAGE_MASK;
 270         addr = start;
 271         len = (unsigned long) nr_pages << PAGE_SHIFT;
 272
 273         end = start + len;
 274         if (end < start)
 275                 goto slow_irqon;
 276
 277         /* XXX: batch / limit 'nr' */
 278         local_irq_disable();
 279         pgdp = pgd_offset(mm, addr);
 280         do {
 281                 pgd_t pgd = *pgdp;
 282
 283                 next = pgd_addr_end(addr, end);
 284                 if (pgd_none(pgd))
 285                         goto slow;
 286                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 287                         goto slow;
 288         } while (pgdp++, addr = next, addr != end);
 289         local_irq_enable();
 290
 291         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 292         return nr;
 293 slow:
 294         local_irq_enable();
 295
 296 slow_irqon:
 297         /* Try to get the remaining pages with get_user_pages */
 298         start += nr << PAGE_SHIFT;
 299         pages += nr;
 300
 301         down_read(&mm->mmap_sem);
 302         ret = get_user_pages(current, mm, start,
 303                                 (end - start) >> PAGE_SHIFT,
 304                                 write, 0, pages, NULL);
 305         up_read(&mm->mmap_sem);
 306
 307         /* Have to be a bit careful with return values */
 308         if (nr > 0) {
 309                 if (ret < 0)
 310                         ret = nr;
 311                 else
 312                         ret += nr;
 313         }
 314         return ret;
 315 }