function category_homepage( $query ) {
	global $wp_the_query;

	if ( $query->is_home() && $query == $wp_the_query ) {
		$query->set( 'tax_query', array( array(
			'taxonomy' => 'category',
			'terms' => 'homepage',
			'field' => 'slug'
		) ) );
	}
}
add_action( 'pre_get_posts', 'category_homepage' );