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/cpu-features.h>
  16 #include <asm/pgtable.h>
  17
  18 static inline pte_t gup_get_pte(pte_t *ptep)
  19 {
  20 #if defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32)
  21         pte_t pte;
  22
  23 retry:
  24         pte.pte_low = ptep->pte_low;
  25         smp_rmb();
  26         pte.pte_high = ptep->pte_high;
  27         smp_rmb();
  28         if (unlikely(pte.pte_low != ptep->pte_low))
  29                 goto retry;
  30
  31         return pte;
  32 #else
  33         return READ_ONCE(*ptep);
  34 #endif
  35 }
  36
  37 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
  38                         int write, struct page **pages, int *nr)
  39 {
  40         pte_t *ptep = pte_offset_map(&pmd, addr);
  41         do {
  42                 pte_t pte = gup_get_pte(ptep);
  43                 struct page *page;
  44
  45                 if (!pte_present(pte) ||
  46                     pte_special(pte) || (write && !pte_write(pte))) {
  47                         pte_unmap(ptep);
  48                         return 0;
  49                 }
  50                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  51                 page = pte_page(pte);
  52                 get_page(page);
  53                 SetPageReferenced(page);
  54                 pages[*nr] = page;
  55                 (*nr)++;
  56
  57         } while (ptep++, addr += PAGE_SIZE, addr != end);
  58
  59         pte_unmap(ptep - 1);
  60         return 1;
  61 }
  62
  63 static inline void get_head_page_multiple(struct page *page, int nr)
  64 {
  65         VM_BUG_ON(page != compound_head(page));
  66         VM_BUG_ON(page_count(page) == 0);
  67         page_ref_add(page, nr);
  68         SetPageReferenced(page);
  69 }
  70
  71 static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
  72                         int write, struct page **pages, int *nr)
  73 {
  74         pte_t pte = *(pte_t *)&pmd;
  75         struct page *head, *page;
  76         int refs;
  77
  78         if (write && !pte_write(pte))
  79                 return 0;
  80         /* hugepages are never "special" */
  81         VM_BUG_ON(pte_special(pte));
  82         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  83
  84         refs = 0;
  85         head = pte_page(pte);
  86         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  87         do {
  88                 VM_BUG_ON(compound_head(page) != head);
  89                 pages[*nr] = page;
  90                 (*nr)++;
  91                 page++;
  92                 refs++;
  93         } while (addr += PAGE_SIZE, addr != end);
  94
  95         get_head_page_multiple(head, refs);
  96         return 1;
  97 }
  98
  99 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 100                         int write, struct page **pages, int *nr)
 101 {
 102         unsigned long next;
 103         pmd_t *pmdp;
 104
 105         pmdp = pmd_offset(&pud, addr);
 106         do {
 107                 pmd_t pmd = *pmdp;
 108
 109                 next = pmd_addr_end(addr, end);
 110                 if (pmd_none(pmd))
 111                         return 0;
 112                 if (unlikely(pmd_huge(pmd))) {
 113                         if (!gup_huge_pmd(pmd, addr, next, write, pages,nr))
 114                                 return 0;
 115                 } else {
 116                         if (!gup_pte_range(pmd, addr, next, write, pages,nr))
 117                                 return 0;
 118                 }
 119         } while (pmdp++, addr = next, addr != end);
 120
 121         return 1;
 122 }
 123
 124 static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
 125                         int write, struct page **pages, int *nr)
 126 {
 127         pte_t pte = *(pte_t *)&pud;
 128         struct page *head, *page;
 129         int refs;
 130
 131         if (write && !pte_write(pte))
 132                 return 0;
 133         /* hugepages are never "special" */
 134         VM_BUG_ON(pte_special(pte));
 135         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 136
 137         refs = 0;
 138         head = pte_page(pte);
 139         page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 140         do {
 141                 VM_BUG_ON(compound_head(page) != head);
 142                 pages[*nr] = page;
 143                 (*nr)++;
 144                 page++;
 145                 refs++;
 146         } while (addr += PAGE_SIZE, addr != end);
 147
 148         get_head_page_multiple(head, refs);
 149         return 1;
 150 }
 151
 152 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 153                         int write, struct page **pages, int *nr)
 154 {
 155         unsigned long next;
 156         pud_t *pudp;
 157
 158         pudp = pud_offset(&pgd, addr);
 159         do {
 160                 pud_t pud = *pudp;
 161
 162                 next = pud_addr_end(addr, end);
 163                 if (pud_none(pud))
 164                         return 0;
 165                 if (unlikely(pud_huge(pud))) {
 166                         if (!gup_huge_pud(pud, addr, next, write, pages,nr))
 167                                 return 0;
 168                 } else {
 169                         if (!gup_pmd_range(pud, addr, next, write, pages,nr))
 170                                 return 0;
 171                 }
 172         } while (pudp++, addr = next, addr != end);
 173
 174         return 1;
 175 }
 176
 177 /*
 178  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 179  * back to the regular GUP.
 180  */
 181 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 182                           struct page **pages)
 183 {
 184         struct mm_struct *mm = current->mm;
 185         unsigned long addr, len, end;
 186         unsigned long next;
 187         unsigned long flags;
 188         pgd_t *pgdp;
 189         int nr = 0;
 190
 191         start &= PAGE_MASK;
 192         addr = start;
 193         len = (unsigned long) nr_pages << PAGE_SHIFT;
 194         end = start + len;
 195         if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
 196                                         (void __user *)start, len)))
 197                 return 0;
 198
 199         /*
 200          * XXX: batch / limit 'nr', to avoid large irq off latency
 201          * needs some instrumenting to determine the common sizes used by
 202          * important workloads (eg. DB2), and whether limiting the batch
 203          * size will decrease performance.
 204          *
 205          * It seems like we're in the clear for the moment. Direct-IO is
 206          * the main guy that batches up lots of get_user_pages, and even
 207          * they are limited to 64-at-a-time which is not so many.
 208          */
 209         /*
 210          * This doesn't prevent pagetable teardown, but does prevent
 211          * the pagetables and pages from being freed.
 212          *
 213          * So long as we atomically load page table pointers versus teardown,
 214          * we can follow the address down to the page and take a ref on it.
 215          */
 216         local_irq_save(flags);
 217         pgdp = pgd_offset(mm, addr);
 218         do {
 219                 pgd_t pgd = *pgdp;
 220
 221                 next = pgd_addr_end(addr, end);
 222                 if (pgd_none(pgd))
 223                         break;
 224                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 225                         break;
 226         } while (pgdp++, addr = next, addr != end);
 227         local_irq_restore(flags);
 228
 229         return nr;
 230 }
 231
 232 /**
 233  * get_user_pages_fast() - pin user pages in memory
 234  * @start:      starting user address
 235  * @nr_pages:   number of pages from start to pin
 236  * @write:      whether pages will be written to
 237  * @pages:      array that receives pointers to the pages pinned.
 238  *              Should be at least nr_pages long.
 239  *
 240  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 241  * If not successful, it will fall back to taking the lock and
 242  * calling get_user_pages().
 243  *
 244  * Returns number of pages pinned. This may be fewer than the number
 245  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 246  * were pinned, returns -errno.
 247  */
 248 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 249                         struct page **pages)
 250 {
 251         struct mm_struct *mm = current->mm;
 252         unsigned long addr, len, end;
 253         unsigned long next;
 254         pgd_t *pgdp;
 255         int ret, nr = 0;
 256
 257         start &= PAGE_MASK;
 258         addr = start;
 259         len = (unsigned long) nr_pages << PAGE_SHIFT;
 260
 261         end = start + len;
 262         if (end < start || cpu_has_dc_aliases)
 263                 goto slow_irqon;
 264
 265         /* XXX: batch / limit 'nr' */
 266         local_irq_disable();
 267         pgdp = pgd_offset(mm, addr);
 268         do {
 269                 pgd_t pgd = *pgdp;
 270
 271                 next = pgd_addr_end(addr, end);
 272                 if (pgd_none(pgd))
 273                         goto slow;
 274                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 275                         goto slow;
 276         } while (pgdp++, addr = next, addr != end);
 277         local_irq_enable();
 278
 279         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 280         return nr;
 281 slow:
 282         local_irq_enable();
 283
 284 slow_irqon:
 285         /* Try to get the remaining pages with get_user_pages */
 286         start += nr << PAGE_SHIFT;
 287         pages += nr;
 288
 289         ret = get_user_pages_unlocked(start, (end - start) >> PAGE_SHIFT,
 290                                       pages, write ? FOLL_WRITE : 0);
 291
 292         /* Have to be a bit careful with return values */
 293         if (nr > 0) {
 294                 if (ret < 0)
 295                         ret = nr;
 296                 else
 297                         ret += nr;
 298         }
 299         return ret;
 300 }