Linux - copy_to_user vs copy_to_user_no_fault

static __always_inline unsigned long __must_check
copy_to_user(void __user *to, const void *from, unsigned long n)
{
	if (!check_copy_size(from, n, true))
		return n;

#ifdef INLINE_COPY_TO_USER
	return _inline_copy_to_user(to, from, n);
#else
	return _copy_to_user(to, from, n);
#endif
}

#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label)	\
	while (len >= sizeof(type)) {					\
		__put_kernel_nofault(dst, src, type, err_label);		\
		dst += sizeof(type);					\
		src += sizeof(type);					\
		len -= sizeof(type);					\
	}

long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
	pagefault_disable();
	copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
	pagefault_enable();
	return 0;
Efault:
	pagefault_enable();
	return -EFAULT;
}

/*
 * These routines enable/disable the pagefault handler. If disabled, it will
 * not take any locks and go straight to the fixup table.
 *
 * User access methods will not sleep when called from a pagefault_disabled()
 * environment.
 */
static inline void pagefault_disable(void)
{
	pagefault_disabled_inc();
	/*
	 * make sure to have issued the store before a pagefault
	 * can hit.
	 */
	barrier();
}
 
static inline void pagefault_enable(void)
{
	/*
	 * make sure to issue those last loads/stores before enabling
	 * the pagefault handler again.
	 */
	barrier();
	pagefault_disabled_dec();
}

copy_to_kernel_nofault不会触发缺页异常