diff --git a/arch/um/drivers/mmapper_kern.c b/arch/um/drivers/mmapper_kern.c
index 6bc73f0e8e29..7e0619c2c2c6 100644
--- a/arch/um/drivers/mmapper_kern.c
+++ b/arch/um/drivers/mmapper_kern.c
@@ -37,13 +37,7 @@ static ssize_t mmapper_write(struct file *file, const char __user *buf,
 	if (*ppos > mmapper_size)
 		return -EINVAL;
 
-	if (count > mmapper_size - *ppos)
-		count = mmapper_size - *ppos;
-
-	if (copy_from_user(&v_buf[*ppos], buf, count))
-		return -EFAULT;
-
-	return count;
+	return simple_write_to_buffer(v_buf, mmapper_size, ppos, buf, count);
 }
 
 static long mmapper_ioctl(struct file *file, unsigned int cmd, unsigned long arg)