arch/sh/mm/gup.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Lockless get_user_pages_fast for SuperH
   4  *
   5  * Copyright (C) 2009 - 2010  Paul Mundt
   6  *
   7  * Cloned from the x86 and PowerPC versions, by:
   8  *
   9  *      Copyright (C) 2008 Nick Piggin
  10  *      Copyright (C) 2008 Novell Inc.
  11  */
  12 #include <linux/sched.h>
  13 #include <linux/mm.h>
  14 #include <linux/vmstat.h>
  15 #include <linux/highmem.h>
  16 #include <asm/pgtable.h>
  17
  18 static inline pte_t gup_get_pte(pte_t *ptep)
  19 {
  20 #ifndef CONFIG_X2TLB
  21         return READ_ONCE(*ptep);
  22 #else
  23         /*
  24          * With get_user_pages_fast, we walk down the pagetables without
  25          * taking any locks.  For this we would like to load the pointers
  26          * atomically, but that is not possible with 64-bit PTEs.  What
  27          * we do have is the guarantee that a pte will only either go
  28          * from not present to present, or present to not present or both
  29          * -- it will not switch to a completely different present page
  30          * without a TLB flush in between; something that we are blocking
  31          * by holding interrupts off.
  32          *
  33          * Setting ptes from not present to present goes:
  34          * ptep->pte_high = h;
  35          * smp_wmb();
  36          * ptep->pte_low = l;
  37          *
  38          * And present to not present goes:
  39          * ptep->pte_low = 0;
  40          * smp_wmb();
  41          * ptep->pte_high = 0;
  42          *
  43          * We must ensure here that the load of pte_low sees l iff pte_high
  44          * sees h. We load pte_high *after* loading pte_low, which ensures we
  45          * don't see an older value of pte_high.  *Then* we recheck pte_low,
  46          * which ensures that we haven't picked up a changed pte high. We might
  47          * have got rubbish values from pte_low and pte_high, but we are
  48          * guaranteed that pte_low will not have the present bit set *unless*
  49          * it is 'l'. And get_user_pages_fast only operates on present ptes, so
  50          * we're safe.
  51          *
  52          * gup_get_pte should not be used or copied outside gup.c without being
  53          * very careful -- it does not atomically load the pte or anything that
  54          * is likely to be useful for you.
  55          */
  56         pte_t pte;
  57
  58 retry:
  59         pte.pte_low = ptep->pte_low;
  60         smp_rmb();
  61         pte.pte_high = ptep->pte_high;
  62         smp_rmb();
  63         if (unlikely(pte.pte_low != ptep->pte_low))
  64                 goto retry;
  65
  66         return pte;
  67 #endif
  68 }
  69
  70 /*
  71  * The performance critical leaf functions are made noinline otherwise gcc
  72  * inlines everything into a single function which results in too much
  73  * register pressure.
  74  */
  75 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
  76                 unsigned long end, int write, struct page **pages, int *nr)
  77 {
  78         u64 mask, result;
  79         pte_t *ptep;
  80
  81 #ifdef CONFIG_X2TLB
  82         result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
  83         if (write)
  84                 result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
  85 #elif defined(CONFIG_SUPERH64)
  86         result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
  87         if (write)
  88                 result |= _PAGE_WRITE;
  89 #else
  90         result = _PAGE_PRESENT | _PAGE_USER;
  91         if (write)
  92                 result |= _PAGE_RW;
  93 #endif
  94
  95         mask = result | _PAGE_SPECIAL;
  96
  97         ptep = pte_offset_map(&pmd, addr);
  98         do {
  99                 pte_t pte = gup_get_pte(ptep);
 100                 struct page *page;
 101
 102                 if ((pte_val(pte) & mask) != result) {
 103                         pte_unmap(ptep);
 104                         return 0;
 105                 }
 106                 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 107                 page = pte_page(pte);
 108                 get_page(page);
 109                 __flush_anon_page(page, addr);
 110                 flush_dcache_page(page);
 111                 pages[*nr] = page;
 112                 (*nr)++;
 113
 114         } while (ptep++, addr += PAGE_SIZE, addr != end);
 115         pte_unmap(ptep - 1);
 116
 117         return 1;
 118 }
 119
 120 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 121                 int write, struct page **pages, int *nr)
 122 {
 123         unsigned long next;
 124         pmd_t *pmdp;
 125
 126         pmdp = pmd_offset(&pud, addr);
 127         do {
 128                 pmd_t pmd = *pmdp;
 129
 130                 next = pmd_addr_end(addr, end);
 131                 if (pmd_none(pmd))
 132                         return 0;
 133                 if (!gup_pte_range(pmd, addr, next, write, pages, nr))
 134                         return 0;
 135         } while (pmdp++, addr = next, addr != end);
 136
 137         return 1;
 138 }
 139
 140 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
 141                         int write, struct page **pages, int *nr)
 142 {
 143         unsigned long next;
 144         pud_t *pudp;
 145
 146         pudp = pud_offset(&pgd, addr);
 147         do {
 148                 pud_t pud = *pudp;
 149
 150                 next = pud_addr_end(addr, end);
 151                 if (pud_none(pud))
 152                         return 0;
 153                 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
 154                         return 0;
 155         } while (pudp++, addr = next, addr != end);
 156
 157         return 1;
 158 }
 159
 160 /*
 161  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
 162  * back to the regular GUP.
 163  * Note a difference with get_user_pages_fast: this always returns the
 164  * number of pages pinned, 0 if no pages were pinned.
 165  */
 166 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 167                           struct page **pages)
 168 {
 169         struct mm_struct *mm = current->mm;
 170         unsigned long addr, len, end;
 171         unsigned long next;
 172         unsigned long flags;
 173         pgd_t *pgdp;
 174         int nr = 0;
 175
 176         start &= PAGE_MASK;
 177         addr = start;
 178         len = (unsigned long) nr_pages << PAGE_SHIFT;
 179         end = start + len;
 180         if (unlikely(!access_ok((void __user *)start, len)))
 181                 return 0;
 182
 183         /*
 184          * This doesn't prevent pagetable teardown, but does prevent
 185          * the pagetables and pages from being freed.
 186          */
 187         local_irq_save(flags);
 188         pgdp = pgd_offset(mm, addr);
 189         do {
 190                 pgd_t pgd = *pgdp;
 191
 192                 next = pgd_addr_end(addr, end);
 193                 if (pgd_none(pgd))
 194                         break;
 195                 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
 196                         break;
 197         } while (pgdp++, addr = next, addr != end);
 198         local_irq_restore(flags);
 199
 200         return nr;
 201 }
 202
 203 /**
 204  * get_user_pages_fast() - pin user pages in memory
 205  * @start:      starting user address
 206  * @nr_pages:   number of pages from start to pin
 207  * @gup_flags:  flags modifying pin behaviour
 208  * @pages:      array that receives pointers to the pages pinned.
 209  *              Should be at least nr_pages long.
 210  *
 211  * Attempt to pin user pages in memory without taking mm->mmap_sem.
 212  * If not successful, it will fall back to taking the lock and
 213  * calling get_user_pages().
 214  *
 215  * Returns number of pages pinned. This may be fewer than the number
 216  * requested. If nr_pages is 0 or negative, returns 0. If no pages
 217  * were pinned, returns -errno.
 218  */
 219 int get_user_pages_fast(unsigned long start, int nr_pages,
 220                         unsigned int gup_flags, struct page **pages)
 221 {
 222         struct mm_struct *mm = current->mm;
 223         unsigned long addr, len, end;
 224         unsigned long next;
 225         pgd_t *pgdp;
 226         int nr = 0;
 227
 228         start &= PAGE_MASK;
 229         addr = start;
 230         len = (unsigned long) nr_pages << PAGE_SHIFT;
 231
 232         end = start + len;
 233         if (end < start)
 234                 goto slow_irqon;
 235
 236         local_irq_disable();
 237         pgdp = pgd_offset(mm, addr);
 238         do {
 239                 pgd_t pgd = *pgdp;
 240
 241                 next = pgd_addr_end(addr, end);
 242                 if (pgd_none(pgd))
 243                         goto slow;
 244                 if (!gup_pud_range(pgd, addr, next, gup_flags & FOLL_WRITE,
 245                                    pages, &nr))
 246                         goto slow;
 247         } while (pgdp++, addr = next, addr != end);
 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                 /* Try to get the remaining pages with get_user_pages */
 260                 start += nr << PAGE_SHIFT;
 261                 pages += nr;
 262
 263                 ret = get_user_pages_unlocked(start,
 264                         (end - start) >> PAGE_SHIFT, pages,
 265                         gup_flags);
 266
 267                 /* Have to be a bit careful with return values */
 268                 if (nr > 0) {
 269                         if (ret < 0)
 270                                 ret = nr;
 271                         else
 272                                 ret += nr;
 273                 }
 274
 275                 return ret;
 276         }
 277 }