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uaccess_with_memcpy.c

/*
 *  linux/arch/arm/lib/uaccess_with_memcpy.c
 *
 *  Written by: Lennert Buytenhek and Nicolas Pitre
 *  Copyright (C) 2009 Marvell Semiconductor
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/ctype.h>
#include <linux/uaccess.h>
#include <linux/rwsem.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/hardirq.h> /* for in_atomic() */
#include <asm/current.h>
#include <asm/page.h>

static int
pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
{
      unsigned long addr = (unsigned long)_addr;
      pgd_t *pgd;
      pmd_t *pmd;
      pte_t *pte;
      spinlock_t *ptl;

      pgd = pgd_offset(current->mm, addr);
      if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
            return 0;

      pmd = pmd_offset(pgd, addr);
      if (unlikely(pmd_none(*pmd) || pmd_bad(*pmd)))
            return 0;

      pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
      if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
          !pte_write(*pte) || !pte_dirty(*pte))) {
            pte_unmap_unlock(pte, ptl);
            return 0;
      }

      *ptep = pte;
      *ptlp = ptl;

      return 1;
}

static unsigned long noinline
__copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
{
      int atomic;

      if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
            memcpy((void *)to, from, n);
            return 0;
      }

      /* the mmap semaphore is taken only if not in an atomic context */
      atomic = in_atomic();

      if (!atomic)
            down_read(&current->mm->mmap_sem);
      while (n) {
            pte_t *pte;
            spinlock_t *ptl;
            int tocopy;

            while (!pin_page_for_write(to, &pte, &ptl)) {
                  if (!atomic)
                        up_read(&current->mm->mmap_sem);
                  if (__put_user(0, (char __user *)to))
                        goto out;
                  if (!atomic)
                        down_read(&current->mm->mmap_sem);
            }

            tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
            if (tocopy > n)
                  tocopy = n;

            memcpy((void *)to, from, tocopy);
            to += tocopy;
            from += tocopy;
            n -= tocopy;

            pte_unmap_unlock(pte, ptl);
      }
      if (!atomic)
            up_read(&current->mm->mmap_sem);

out:
      return n;
}

unsigned long
__copy_to_user(void __user *to, const void *from, unsigned long n)
{
      /*
       * This test is stubbed out of the main function above to keep
       * the overhead for small copies low by avoiding a large
       * register dump on the stack just to reload them right away.
       * With frame pointer disabled, tail call optimization kicks in
       * as well making this test almost invisible.
       */
      if (n < 64)
            return __copy_to_user_std(to, from, n);
      return __copy_to_user_memcpy(to, from, n);
}
      
static unsigned long noinline
__clear_user_memset(void __user *addr, unsigned long n)
{
      if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
            memset((void *)addr, 0, n);
            return 0;
      }

      down_read(&current->mm->mmap_sem);
      while (n) {
            pte_t *pte;
            spinlock_t *ptl;
            int tocopy;

            while (!pin_page_for_write(addr, &pte, &ptl)) {
                  up_read(&current->mm->mmap_sem);
                  if (__put_user(0, (char __user *)addr))
                        goto out;
                  down_read(&current->mm->mmap_sem);
            }

            tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
            if (tocopy > n)
                  tocopy = n;

            memset((void *)addr, 0, tocopy);
            addr += tocopy;
            n -= tocopy;

            pte_unmap_unlock(pte, ptl);
      }
      up_read(&current->mm->mmap_sem);

out:
      return n;
}

unsigned long __clear_user(void __user *addr, unsigned long n)
{
      /* See rational for this in __copy_to_user() above. */
      if (n < 64)
            return __clear_user_std(addr, n);
      return __clear_user_memset(addr, n);
}

#if 0

/*
 * This code is disabled by default, but kept around in case the chosen
 * thresholds need to be revalidated.  Some overhead (small but still)
 * would be implied by a runtime determined variable threshold, and
 * so far the measurement on concerned targets didn't show a worthwhile
 * variation.
 *
 * Note that a fairly precise sched_clock() implementation is needed
 * for results to make some sense.
 */

#include <linux/vmalloc.h>

static int __init test_size_treshold(void)
{
      struct page *src_page, *dst_page;
      void *user_ptr, *kernel_ptr;
      unsigned long long t0, t1, t2;
      int size, ret;

      ret = -ENOMEM;
      src_page = alloc_page(GFP_KERNEL);
      if (!src_page)
            goto no_src;
      dst_page = alloc_page(GFP_KERNEL);
      if (!dst_page)
            goto no_dst;
      kernel_ptr = page_address(src_page);
      user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
      if (!user_ptr)
            goto no_vmap;

      /* warm up the src page dcache */
      ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);

      for (size = PAGE_SIZE; size >= 4; size /= 2) {
            t0 = sched_clock();
            ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
            t1 = sched_clock();
            ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
            t2 = sched_clock();
            printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
      }

      for (size = PAGE_SIZE; size >= 4; size /= 2) {
            t0 = sched_clock();
            ret |= __clear_user_memset(user_ptr, size);
            t1 = sched_clock();
            ret |= __clear_user_std(user_ptr, size);
            t2 = sched_clock();
            printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
      }

      if (ret)
            ret = -EFAULT;

      vunmap(user_ptr);
no_vmap:
      put_page(dst_page);
no_dst:
      put_page(src_page);
no_src:
      return ret;
}

subsys_initcall(test_size_treshold);

#endif

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