keys (torch.Tensor): [N, S2, H, D]
            values (torch.Tensor): [N, S2, H, D]
            q_mask (torch.Tensor): [N, S1] (optional)
            kv_mask (torch.Tensor): [N, S2] (optional)
        Returns:
            queried_values (torch.Tensor): [N, S1, H, D]
        Nr"