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.
  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                         spin_unlock(ptl);
  63                         return 0;
  64                 }
  65
  66                 *ptep = NULL;
  67                 *ptlp = ptl;
  68                 return 1;
  69         }
  70
  71         if (unlikely(pmd_bad(*pmd)))
  72                 return 0;
  73
  74         pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
  75         if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
  76             !pte_write(*pte) || !pte_dirty(*pte))) {
  77                 pte_unmap_unlock(pte, ptl);
  78                 return 0;
  79         }
  80
  81         *ptep = pte;
  82         *ptlp = ptl;
  83
  84         return 1;
  85 }
  86
  87 static unsigned long noinline
  88 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
  89 {
  90         unsigned long ua_flags;
  91         int atomic;
  92
  93         if (uaccess_kernel()) {
  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 = faulthandler_disabled();
 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                 ua_flags = uaccess_save_and_enable();
 122                 memcpy((void *)to, from, tocopy);
 123                 uaccess_restore(ua_flags);
 124                 to += tocopy;
 125                 from += tocopy;
 126                 n -= tocopy;
 127
 128                 if (pte)
 129                         pte_unmap_unlock(pte, ptl);
 130                 else
 131                         spin_unlock(ptl);
 132         }
 133         if (!atomic)
 134                 up_read(&current->mm->mmap_sem);
 135
 136 out:
 137         return n;
 138 }
 139
 140 unsigned long
 141 arm_copy_to_user(void __user *to, const void *from, unsigned long n)
 142 {
 143         /*
 144          * This test is stubbed out of the main function above to keep
 145          * the overhead for small copies low by avoiding a large
 146          * register dump on the stack just to reload them right away.
 147          * With frame pointer disabled, tail call optimization kicks in
 148          * as well making this test almost invisible.
 149          */
 150         if (n < 64) {
 151                 unsigned long ua_flags = uaccess_save_and_enable();
 152                 n = __copy_to_user_std(to, from, n);
 153                 uaccess_restore(ua_flags);
 154         } else {
 155                 n = __copy_to_user_memcpy(uaccess_mask_range_ptr(to, n),
 156                                           from, n);
 157         }
 158         return n;
 159 }
 160
 161 static unsigned long noinline
 162 __clear_user_memset(void __user *addr, unsigned long n)
 163 {
 164         unsigned long ua_flags;
 165
 166         if (uaccess_kernel()) {
 167                 memset((void *)addr, 0, n);
 168                 return 0;
 169         }
 170
 171         down_read(&current->mm->mmap_sem);
 172         while (n) {
 173                 pte_t *pte;
 174                 spinlock_t *ptl;
 175                 int tocopy;
 176
 177                 while (!pin_page_for_write(addr, &pte, &ptl)) {
 178                         up_read(&current->mm->mmap_sem);
 179                         if (__put_user(0, (char __user *)addr))
 180                                 goto out;
 181                         down_read(&current->mm->mmap_sem);
 182                 }
 183
 184                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
 185                 if (tocopy > n)
 186                         tocopy = n;
 187
 188                 ua_flags = uaccess_save_and_enable();
 189                 memset((void *)addr, 0, tocopy);
 190                 uaccess_restore(ua_flags);
 191                 addr += tocopy;
 192                 n -= tocopy;
 193
 194                 if (pte)
 195                         pte_unmap_unlock(pte, ptl);
 196                 else
 197                         spin_unlock(ptl);
 198         }
 199         up_read(&current->mm->mmap_sem);
 200
 201 out:
 202         return n;
 203 }
 204
 205 unsigned long arm_clear_user(void __user *addr, unsigned long n)
 206 {
 207         /* See rational for this in __copy_to_user() above. */
 208         if (n < 64) {
 209                 unsigned long ua_flags = uaccess_save_and_enable();
 210                 n = __clear_user_std(addr, n);
 211                 uaccess_restore(ua_flags);
 212         } else {
 213                 n = __clear_user_memset(addr, n);
 214         }
 215         return n;
 216 }
 217
 218 #if 0
 219
 220 /*
 221  * This code is disabled by default, but kept around in case the chosen
 222  * thresholds need to be revalidated.  Some overhead (small but still)
 223  * would be implied by a runtime determined variable threshold, and
 224  * so far the measurement on concerned targets didn't show a worthwhile
 225  * variation.
 226  *
 227  * Note that a fairly precise sched_clock() implementation is needed
 228  * for results to make some sense.
 229  */
 230
 231 #include <linux/vmalloc.h>
 232
 233 static int __init test_size_treshold(void)
 234 {
 235         struct page *src_page, *dst_page;
 236         void *user_ptr, *kernel_ptr;
 237         unsigned long long t0, t1, t2;
 238         int size, ret;
 239
 240         ret = -ENOMEM;
 241         src_page = alloc_page(GFP_KERNEL);
 242         if (!src_page)
 243                 goto no_src;
 244         dst_page = alloc_page(GFP_KERNEL);
 245         if (!dst_page)
 246                 goto no_dst;
 247         kernel_ptr = page_address(src_page);
 248         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
 249         if (!user_ptr)
 250                 goto no_vmap;
 251
 252         /* warm up the src page dcache */
 253         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
 254
 255         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 256                 t0 = sched_clock();
 257                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
 258                 t1 = sched_clock();
 259                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
 260                 t2 = sched_clock();
 261                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 262         }
 263
 264         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 265                 t0 = sched_clock();
 266                 ret |= __clear_user_memset(user_ptr, size);
 267                 t1 = sched_clock();
 268                 ret |= __clear_user_std(user_ptr, size);
 269                 t2 = sched_clock();
 270                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 271         }
 272
 273         if (ret)
 274                 ret = -EFAULT;
 275
 276         vunmap(user_ptr);
 277 no_vmap:
 278         put_page(dst_page);
 279 no_dst:
 280         put_page(src_page);
 281 no_src:
 282         return ret;
 283 }
 284
 285 subsys_initcall(test_size_treshold);
 286
 287 #endif