arch/mips/mm/gup.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Lockless get_user_pages_fast for MIPS
   4  *
   5  * Copyright (C) 2008 Nick Piggin
   6  * Copyright (C) 2008 Novell Inc.
   7  * Copyright (C) 2011 Ralf Baechle
   8  */
   9 #include <linux/sched.h>
  10 #include <linux/mm.h>
  11 #include <linux/vmstat.h>
  12 #include <linux/highmem.h>
  13 #include <linux/swap.h>
  14 #include <linux/hugetlb.h>
  15
  16 #include <asm/cpu-features.h>
  17 #include <asm/pgtable.h>
  18
  19 static inline pte_t gup_get_pte(pte_t *ptep)
  20 {
  21 #if defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32)
  22         pte_t pte;
  23
  24 retry:
  25         pte.pte_low = ptep->pte_low;
  26         smp_rmb();
  27         pte.pte_high = ptep->pte_high;
  28         smp_rmb();
  29         if (unlikely(pte.pte_low != ptep->pte_low))
  30                 goto retry;
  31
  32         return pte;
  33 #else
  34         return READ_ONCE(*ptep);
  35 #endif
  36 }
  37
  38 static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
  39                         int write, struct page **pages, int *nr)
  40 {
  41         pte_t *ptep = pte_offset_map(&pmd, addr);
  42         do {
  43                 pte_t pte = gup_get_pte(ptep);
  44                 struct page *page;
  45
  46                 if (!pte_present(pte) ||
  47                     pte_special(pte) || (write && !pte_write(pte))) {
  48                         pte_unmap(ptep);
  49                         return 0;
  50                 }
  51                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  52                 page = pte_page(pte);
  53                 get_page(page);
  54                 SetPageReferenced(page);
  55                 pages[*nr] = page;
  56                 (*nr)++;
  57
  58         } while (ptep++, addr += PAGE_SIZE, addr != end);
  59
  60         pte_unmap(ptep - 1);
  61         return 1;
  62 }
  63
  64 static inline void get_head_page_multiple(struct page *page, int nr)
  65 {
  66         VM_BUG_ON(page != compound_head(page));
  67         VM_BUG_ON(page_count(page) == 0);
  68         page_ref_add(page, nr);
  69         SetPageReferenced(page);
  70 }
  71
  72 static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
  73                         int write, struct page **pages, int *nr)
  74 {
  75         pte_t pte = *(pte_t *)&pmd;
  76         struct page *head, *page;
  77         int refs;
  78
  79         if (write && !pte_write(pte))
  80                 return 0;
  81         /* hugepages are never "special" */
  82         VM_BUG_ON(pte_special(pte));
  83         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
  84
  85         refs = 0;
  86         head = pte_page(pte);
  87         page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
  88         do {
  89                 VM_BUG_ON(compound_head(page) != head);
  90                 pages[*nr] = 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                 if (pmd_none(pmd))
 112                         return 0;
 113                 if (unlikely(pmd_huge(pmd))) {
 114                         if (!gup_huge_pmd(pmd, addr, next, write, pages,nr))
 115                                 return 0;
 116                 } else {
 117                         if (!gup_pte_range(pmd, addr, next, write, pages,nr))
 118                                 return 0;
 119                 }
 120         } while (pmdp++, addr = next, addr != end);
 121
 122         return 1;
 123 }
 124
 125 static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
 126                         int write, struct page **pages, int *nr)
 127 {
 128         pte_t pte = *(pte_t *)&pud;
 129         struct page *head, *page;
 130         int refs;
 131
 132         if (write && !pte_write(pte))
 133                 return 0;
 134         /* hugepages are never "special" */
 135         VM_BUG_ON(pte_special(pte));
 136         VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 137
 138         refs = 0;
 139         head = pte_page(pte);
 140         page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
 141         do {
 142                 VM_BUG_ON(compound_head(page) != head);
 143                 pages[*nr] = page;
 144                 (*nr)++;
 145                 page++;
 146                 refs++;
 147         } while (addr += PAGE_SIZE, addr != end);
 148
 149         get_head_page_multiple(head, refs);
 150         return 1;
 151 }
 152
 153 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 154                         int write, struct page **pages, int *nr)
 155 {
 156         unsigned long next;
 157         pud_t *pudp;
 158
 159         pudp = pud_offset(&pgd, addr);
 160         do {
 161                 pud_t pud = *pudp;
 162
 163                 next = pud_addr_end(addr, end);
 164                 if (pud_none(pud))
 165                         return 0;
 166                 if (unlikely(pud_huge(pud))) {
 167                         if (!gup_huge_pud(pud, addr, next, write, pages,nr))
 168                                 return 0;
 169                 } else {
 170                         if (!gup_pmd_range(pud, addr, next, write, pages,nr))
 171                                 return 0;
 172                 }
 173         } while (pudp++, addr = next, addr != end);
 174
 175         return 1;
 176 }
 177
 178 /*
 179  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 180  * back to the regular GUP.
 181  * Note a difference with get_user_pages_fast: this always returns the
 182  * number of pages pinned, 0 if no pages were pinned.
 183  */
 184 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 185                           struct page **pages)
 186 {
 187         struct mm_struct *mm = current->mm;
 188         unsigned long addr, len, end;
 189         unsigned long next;
 190         unsigned long flags;
 191         pgd_t *pgdp;
 192         int nr = 0;
 193
 194         start &= PAGE_MASK;
 195         addr = start;
 196         len = (unsigned long) nr_pages << PAGE_SHIFT;
 197         end = start + len;
 198         if (unlikely(!access_ok((void __user *)start, len)))
 199                 return 0;
 200
 201         /*
 202          * XXX: batch / limit 'nr', to avoid large irq off latency
 203          * needs some instrumenting to determine the common sizes used by
 204          * important workloads (eg. DB2), and whether limiting the batch
 205          * size will decrease performance.
 206          *
 207          * It seems like we're in the clear for the moment. Direct-IO is
 208          * the main guy that batches up lots of get_user_pages, and even
 209          * they are limited to 64-at-a-time which is not so many.
 210          */
 211         /*
 212          * This doesn't prevent pagetable teardown, but does prevent
 213          * the pagetables and pages from being freed.
 214          *
 215          * So long as we atomically load page table pointers versus teardown,
 216          * we can follow the address down to the page and take a ref on it.
 217          */
 218         local_irq_save(flags);
 219         pgdp = pgd_offset(mm, addr);
 220         do {
 221                 pgd_t pgd = *pgdp;
 222
 223                 next = pgd_addr_end(addr, end);
 224                 if (pgd_none(pgd))
 225                         break;
 226                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 227                         break;
 228         } while (pgdp++, addr = next, addr != end);
 229         local_irq_restore(flags);
 230
 231         return nr;
 232 }
 233
 234 /**
 235  * get_user_pages_fast() - pin user pages in memory
 236  * @start:      starting user address
 237  * @nr_pages:   number of pages from start to pin
 238  * @gup_flags:  flags modifying pin behaviour
 239  * @pages:      array that receives pointers to the pages pinned.
 240  *              Should be at least nr_pages long.
 241  *
 242  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 243  * If not successful, it will fall back to taking the lock and
 244  * calling get_user_pages().
 245  *
 246  * Returns number of pages pinned. This may be fewer than the number
 247  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 248  * were pinned, returns -errno.
 249  */
 250 int get_user_pages_fast(unsigned long start, int nr_pages,
 251                         unsigned int gup_flags, struct page **pages)
 252 {
 253         struct mm_struct *mm = current->mm;
 254         unsigned long addr, len, end;
 255         unsigned long next;
 256         pgd_t *pgdp;
 257         int ret, nr = 0;
 258
 259         start &= PAGE_MASK;
 260         addr = start;
 261         len = (unsigned long) nr_pages << PAGE_SHIFT;
 262
 263         end = start + len;
 264         if (end < start || cpu_has_dc_aliases)
 265                 goto slow_irqon;
 266
 267         /* XXX: batch / limit 'nr' */
 268         local_irq_disable();
 269         pgdp = pgd_offset(mm, addr);
 270         do {
 271                 pgd_t pgd = *pgdp;
 272
 273                 next = pgd_addr_end(addr, end);
 274                 if (pgd_none(pgd))
 275                         goto slow;
 276                 if (!gup_pud_range(pgd, addr, next, gup_flags & FOLL_WRITE,
 277                                    pages, &nr))
 278                         goto slow;
 279         } while (pgdp++, addr = next, addr != end);
 280         local_irq_enable();
 281
 282         VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
 283         return nr;
 284 slow:
 285         local_irq_enable();
 286
 287 slow_irqon:
 288         /* Try to get the remaining pages with get_user_pages */
 289         start += nr << PAGE_SHIFT;
 290         pages += nr;
 291
 292         ret = get_user_pages_unlocked(start, (end - start) >> PAGE_SHIFT,
 293                                       pages, gup_flags);
 294
 295         /* Have to be a bit careful with return values */
 296         if (nr > 0) {
 297                 if (ret < 0)
 298                         ret = nr;
 299                 else
 300                         ret += nr;
 301         }
 302         return ret;
 303 }