usercopy.c

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/*
 * User address space access functions.
 *
 *  For licencing details see kernel-base/COPYING
 */

#include <linux/highmem.h>
#include <linux/module.h>

#include <asm/word-at-a-time.h>
#include <linux/sched.h>

/*
 * best effort, GUP based copy_from_user() that is NMI-safe
 */
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
{
    unsigned long offset, addr = (unsigned long)from;
    unsigned long size, len = 0;
    struct page *page;
    void *map;
    int ret;

    if (__range_not_ok(from, n, TASK_SIZE))
        return len;

    do {
        ret = __get_user_pages_fast(addr, 1, 0, &page);
        if (!ret)
            break;

        offset = addr & (PAGE_SIZE - 1);
        size = min(PAGE_SIZE - offset, n - len);

        map = kmap_atomic(page);
        memcpy(to, map+offset, size);
        kunmap_atomic(map);
        put_page(page);

        len  += size;
        to   += size;
        addr += size;

    } while (len < n);

    return len;
}
EXPORT_SYMBOL_GPL(copy_from_user_nmi);