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Linux/arch/arm/lib/uaccess_with_memcpy.c

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  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 (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 = 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(to, from, n);
156         }
157         return n;
158 }
159         
160 static unsigned long noinline
161 __clear_user_memset(void __user *addr, unsigned long n)
162 {
163         unsigned long ua_flags;
164 
165         if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
166                 memset((void *)addr, 0, n);
167                 return 0;
168         }
169 
170         down_read(&current->mm->mmap_sem);
171         while (n) {
172                 pte_t *pte;
173                 spinlock_t *ptl;
174                 int tocopy;
175 
176                 while (!pin_page_for_write(addr, &pte, &ptl)) {
177                         up_read(&current->mm->mmap_sem);
178                         if (__put_user(0, (char __user *)addr))
179                                 goto out;
180                         down_read(&current->mm->mmap_sem);
181                 }
182 
183                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
184                 if (tocopy > n)
185                         tocopy = n;
186 
187                 ua_flags = uaccess_save_and_enable();
188                 memset((void *)addr, 0, tocopy);
189                 uaccess_restore(ua_flags);
190                 addr += tocopy;
191                 n -= tocopy;
192 
193                 if (pte)
194                         pte_unmap_unlock(pte, ptl);
195                 else
196                         spin_unlock(ptl);
197         }
198         up_read(&current->mm->mmap_sem);
199 
200 out:
201         return n;
202 }
203 
204 unsigned long arm_clear_user(void __user *addr, unsigned long n)
205 {
206         /* See rational for this in __copy_to_user() above. */
207         if (n < 64) {
208                 unsigned long ua_flags = uaccess_save_and_enable();
209                 n = __clear_user_std(addr, n);
210                 uaccess_restore(ua_flags);
211         } else {
212                 n = __clear_user_memset(addr, n);
213         }
214         return n;
215 }
216 
217 #if 0
218 
219 /*
220  * This code is disabled by default, but kept around in case the chosen
221  * thresholds need to be revalidated.  Some overhead (small but still)
222  * would be implied by a runtime determined variable threshold, and
223  * so far the measurement on concerned targets didn't show a worthwhile
224  * variation.
225  *
226  * Note that a fairly precise sched_clock() implementation is needed
227  * for results to make some sense.
228  */
229 
230 #include <linux/vmalloc.h>
231 
232 static int __init test_size_treshold(void)
233 {
234         struct page *src_page, *dst_page;
235         void *user_ptr, *kernel_ptr;
236         unsigned long long t0, t1, t2;
237         int size, ret;
238 
239         ret = -ENOMEM;
240         src_page = alloc_page(GFP_KERNEL);
241         if (!src_page)
242                 goto no_src;
243         dst_page = alloc_page(GFP_KERNEL);
244         if (!dst_page)
245                 goto no_dst;
246         kernel_ptr = page_address(src_page);
247         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
248         if (!user_ptr)
249                 goto no_vmap;
250 
251         /* warm up the src page dcache */
252         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
253 
254         for (size = PAGE_SIZE; size >= 4; size /= 2) {
255                 t0 = sched_clock();
256                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
257                 t1 = sched_clock();
258                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
259                 t2 = sched_clock();
260                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
261         }
262 
263         for (size = PAGE_SIZE; size >= 4; size /= 2) {
264                 t0 = sched_clock();
265                 ret |= __clear_user_memset(user_ptr, size);
266                 t1 = sched_clock();
267                 ret |= __clear_user_std(user_ptr, size);
268                 t2 = sched_clock();
269                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
270         }
271 
272         if (ret)
273                 ret = -EFAULT;
274 
275         vunmap(user_ptr);
276 no_vmap:
277         put_page(dst_page);
278 no_dst:
279         put_page(src_page);
280 no_src:
281         return ret;
282 }
283 
284 subsys_initcall(test_size_treshold);
285 
286 #endif
287 

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