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* linux/arch/arm/lib/uaccess_with_memcpy.c
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* Written by: Lennert Buytenhek and Nicolas Pitre
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* Copyright (C) 2009 Marvell Semiconductor
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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#include <linux/kernel.h>
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#include <linux/ctype.h>
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#include <linux/uaccess.h>
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#include <linux/rwsem.h>
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#include <linux/sched.h>
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#include <linux/hardirq.h> /* for in_atomic() */
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#include <linux/gfp.h>
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#include <linux/highmem.h>
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#include <asm/current.h>
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pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
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unsigned long addr = (unsigned long)_addr;
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pgd = pgd_offset(current->mm, addr);
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if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
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pud = pud_offset(pgd, addr);
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if (unlikely(pud_none(*pud) || pud_bad(*pud)))
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pmd = pmd_offset(pud, addr);
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if (unlikely(pmd_none(*pmd) || pmd_bad(*pmd)))
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pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
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if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
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!pte_write(*pte) || !pte_dirty(*pte))) {
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pte_unmap_unlock(pte, ptl);
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static unsigned long noinline
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__copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
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if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
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memcpy((void *)to, from, n);
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/* the mmap semaphore is taken only if not in an atomic context */
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down_read(¤t->mm->mmap_sem);
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while (!pin_page_for_write(to, &pte, &ptl)) {
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up_read(¤t->mm->mmap_sem);
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if (__put_user(0, (char __user *)to))
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down_read(¤t->mm->mmap_sem);
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tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
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memcpy((void *)to, from, tocopy);
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pte_unmap_unlock(pte, ptl);
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up_read(¤t->mm->mmap_sem);
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__copy_to_user(void __user *to, const void *from, unsigned long n)
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* This test is stubbed out of the main function above to keep
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* the overhead for small copies low by avoiding a large
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* register dump on the stack just to reload them right away.
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* With frame pointer disabled, tail call optimization kicks in
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* as well making this test almost invisible.
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return __copy_to_user_std(to, from, n);
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return __copy_to_user_memcpy(to, from, n);
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static unsigned long noinline
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__clear_user_memset(void __user *addr, unsigned long n)
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if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
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memset((void *)addr, 0, n);
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down_read(¤t->mm->mmap_sem);
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while (!pin_page_for_write(addr, &pte, &ptl)) {
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up_read(¤t->mm->mmap_sem);
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if (__put_user(0, (char __user *)addr))
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down_read(¤t->mm->mmap_sem);
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tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
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memset((void *)addr, 0, tocopy);
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pte_unmap_unlock(pte, ptl);
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up_read(¤t->mm->mmap_sem);
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unsigned long __clear_user(void __user *addr, unsigned long n)
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/* See rational for this in __copy_to_user() above. */
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return __clear_user_std(addr, n);
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return __clear_user_memset(addr, n);
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* This code is disabled by default, but kept around in case the chosen
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* thresholds need to be revalidated. Some overhead (small but still)
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* would be implied by a runtime determined variable threshold, and
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* so far the measurement on concerned targets didn't show a worthwhile
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* Note that a fairly precise sched_clock() implementation is needed
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* for results to make some sense.
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#include <linux/vmalloc.h>
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static int __init test_size_treshold(void)
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struct page *src_page, *dst_page;
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void *user_ptr, *kernel_ptr;
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unsigned long long t0, t1, t2;
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src_page = alloc_page(GFP_KERNEL);
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dst_page = alloc_page(GFP_KERNEL);
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kernel_ptr = page_address(src_page);
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user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
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/* warm up the src page dcache */
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ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
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for (size = PAGE_SIZE; size >= 4; size /= 2) {
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ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
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ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
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printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
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for (size = PAGE_SIZE; size >= 4; size /= 2) {
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ret |= __clear_user_memset(user_ptr, size);
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ret |= __clear_user_std(user_ptr, size);
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printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
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subsys_initcall(test_size_treshold);