arch/arm/lib/uaccess_with_memcpy.c

   1 /*
   2  *  linux/arch/arm/lib/uaccess_with_memcpy.c
   3  *
   4  *  Written by: Lennert Buytenhek and Nicolas Pitre
   5  *  Copyright (C) 2009 Marvell Semiconductor
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/kernel.h>
  13 #include <linux/ctype.h>
  14 #include <linux/uaccess.h>
  15 #include <linux/rwsem.h>
  16 #include <linux/mm.h>
  17 #include <linux/sched.h>
  18 #include <linux/hardirq.h> /* for in_atomic() */
  19 #include <linux/gfp.h>
  20 #include <linux/highmem.h>
  21 #include <linux/hugetlb.h>
  22 #include <asm/current.h>
  23 #include <asm/page.h>
  24
  25 static int
  26 pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
  27 {
  28         unsigned long addr = (unsigned long)_addr;
  29         pgd_t *pgd;
  30         pmd_t *pmd;
  31         pte_t *pte;
  32         pud_t *pud;
  33         spinlock_t *ptl;
  34
  35         pgd = pgd_offset(current->mm, addr);
  36         if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
  37                 return 0;
  38
  39         pud = pud_offset(pgd, addr);
  40         if (unlikely(pud_none(*pud) || pud_bad(*pud)))
  41                 return 0;
  42
  43         pmd = pmd_offset(pud, addr);
  44         if (unlikely(pmd_none(*pmd)))
  45                 return 0;
  46
  47         /*
  48          * A pmd can be bad if it refers to a HugeTLB or THP page.
  49          *
  50          * Both THP and HugeTLB pages have the same pmd layout
  51          * and should not be manipulated by the pte functions.
  52          *
  53          * Lock the page table for the destination and check
  54          * to see that it's still huge and whether or not we will
  55          * need to fault on write, or if we have a splitting THP.
  56          */
  57         if (unlikely(pmd_thp_or_huge(*pmd))) {
  58                 ptl = &current->mm->page_table_lock;
  59                 spin_lock(ptl);
  60                 if (unlikely(!pmd_thp_or_huge(*pmd)
  61                         || pmd_hugewillfault(*pmd)
  62                         || pmd_trans_splitting(*pmd))) {
  63                         spin_unlock(ptl);
  64                         return 0;
  65                 }
  66
  67                 *ptep = NULL;
  68                 *ptlp = ptl;
  69                 return 1;
  70         }
  71
  72         if (unlikely(pmd_bad(*pmd)))
  73                 return 0;
  74
  75         pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
  76         if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
  77             !pte_write(*pte) || !pte_dirty(*pte))) {
  78                 pte_unmap_unlock(pte, ptl);
  79                 return 0;
  80         }
  81
  82         *ptep = pte;
  83         *ptlp = ptl;
  84
  85         return 1;
  86 }
  87
  88 static unsigned long noinline
  89 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
  90 {
  91         int atomic;
  92
  93         if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
  94                 memcpy((void *)to, from, n);
  95                 return 0;
  96         }
  97
  98         /* the mmap semaphore is taken only if not in an atomic context */
  99         atomic = in_atomic();
 100
 101         if (!atomic)
 102                 down_read(&current->mm->mmap_sem);
 103         while (n) {
 104                 pte_t *pte;
 105                 spinlock_t *ptl;
 106                 int tocopy;
 107
 108                 while (!pin_page_for_write(to, &pte, &ptl)) {
 109                         if (!atomic)
 110                                 up_read(&current->mm->mmap_sem);
 111                         if (__put_user(0, (char __user *)to))
 112                                 goto out;
 113                         if (!atomic)
 114                                 down_read(&current->mm->mmap_sem);
 115                 }
 116
 117                 tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
 118                 if (tocopy > n)
 119                         tocopy = n;
 120
 121                 memcpy((void *)to, from, tocopy);
 122                 to += tocopy;
 123                 from += tocopy;
 124                 n -= tocopy;
 125
 126                 if (pte)
 127                         pte_unmap_unlock(pte, ptl);
 128                 else
 129                         spin_unlock(ptl);
 130         }
 131         if (!atomic)
 132                 up_read(&current->mm->mmap_sem);
 133
 134 out:
 135         return n;
 136 }
 137
 138 unsigned long
 139 __copy_to_user(void __user *to, const void *from, unsigned long n)
 140 {
 141         /*
 142          * This test is stubbed out of the main function above to keep
 143          * the overhead for small copies low by avoiding a large
 144          * register dump on the stack just to reload them right away.
 145          * With frame pointer disabled, tail call optimization kicks in
 146          * as well making this test almost invisible.
 147          */
 148         if (n < 64)
 149                 return __copy_to_user_std(to, from, n);
 150         return __copy_to_user_memcpy(to, from, n);
 151 }
 152
 153 static unsigned long noinline
 154 __clear_user_memset(void __user *addr, unsigned long n)
 155 {
 156         if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
 157                 memset((void *)addr, 0, n);
 158                 return 0;
 159         }
 160
 161         down_read(&current->mm->mmap_sem);
 162         while (n) {
 163                 pte_t *pte;
 164                 spinlock_t *ptl;
 165                 int tocopy;
 166
 167                 while (!pin_page_for_write(addr, &pte, &ptl)) {
 168                         up_read(&current->mm->mmap_sem);
 169                         if (__put_user(0, (char __user *)addr))
 170                                 goto out;
 171                         down_read(&current->mm->mmap_sem);
 172                 }
 173
 174                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
 175                 if (tocopy > n)
 176                         tocopy = n;
 177
 178                 memset((void *)addr, 0, tocopy);
 179                 addr += tocopy;
 180                 n -= tocopy;
 181
 182                 if (pte)
 183                         pte_unmap_unlock(pte, ptl);
 184                 else
 185                         spin_unlock(ptl);
 186         }
 187         up_read(&current->mm->mmap_sem);
 188
 189 out:
 190         return n;
 191 }
 192
 193 unsigned long __clear_user(void __user *addr, unsigned long n)
 194 {
 195         /* See rational for this in __copy_to_user() above. */
 196         if (n < 64)
 197                 return __clear_user_std(addr, n);
 198         return __clear_user_memset(addr, n);
 199 }
 200
 201 #if 0
 202
 203 /*
 204  * This code is disabled by default, but kept around in case the chosen
 205  * thresholds need to be revalidated.  Some overhead (small but still)
 206  * would be implied by a runtime determined variable threshold, and
 207  * so far the measurement on concerned targets didn't show a worthwhile
 208  * variation.
 209  *
 210  * Note that a fairly precise sched_clock() implementation is needed
 211  * for results to make some sense.
 212  */
 213
 214 #include <linux/vmalloc.h>
 215
 216 static int __init test_size_treshold(void)
 217 {
 218         struct page *src_page, *dst_page;
 219         void *user_ptr, *kernel_ptr;
 220         unsigned long long t0, t1, t2;
 221         int size, ret;
 222
 223         ret = -ENOMEM;
 224         src_page = alloc_page(GFP_KERNEL);
 225         if (!src_page)
 226                 goto no_src;
 227         dst_page = alloc_page(GFP_KERNEL);
 228         if (!dst_page)
 229                 goto no_dst;
 230         kernel_ptr = page_address(src_page);
 231         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
 232         if (!user_ptr)
 233                 goto no_vmap;
 234
 235         /* warm up the src page dcache */
 236         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
 237
 238         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 239                 t0 = sched_clock();
 240                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
 241                 t1 = sched_clock();
 242                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
 243                 t2 = sched_clock();
 244                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 245         }
 246
 247         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 248                 t0 = sched_clock();
 249                 ret |= __clear_user_memset(user_ptr, size);
 250                 t1 = sched_clock();
 251                 ret |= __clear_user_std(user_ptr, size);
 252                 t2 = sched_clock();
 253                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 254         }
 255
 256         if (ret)
 257                 ret = -EFAULT;
 258
 259         vunmap(user_ptr);
 260 no_vmap:
 261         put_page(dst_page);
 262 no_dst:
 263         put_page(src_page);
 264 no_src:
 265         return ret;
 266 }
 267
 268 subsys_initcall(test_size_treshold);
 269
 270 #endif