/*
   *  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 <linux/gfp.h>

  #include <linux/highmem.h>

  #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;

  	pud_t *pud;

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

  	pud = pud_offset(pgd, addr);
  	if (unlikely(pud_none(*pud) || pud_bad(*pud)))
  		return 0;
  
  	pmd = pmd_offset(pud, 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
  ", 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
  ", 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