uaccess_with_memcpy.c

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/*
 *  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\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