Restrict admin access to certain pages for certain users

This code seems to work well for me (in functions.php):

$user_id = get_current_user_id();
if ($user_id == 2) {
    add_filter( 'parse_query', 'exclude_pages_from_admin' );
}

function exclude_pages_from_admin($query) {
    global $pagenow,$post_type;
    if (is_admin() && $pagenow=='edit.php' && $post_type =='page') {
        $query->query_vars['post__not_in'] = array('123','234','345');
    }
}