In this paper, we consider robust MIMO precoding designs against deterministic imperfect channel state information at the transmitter (CSIT). In contrast to the existing works based on one or two particular channel uncertainty models, we consider a general uncertainty set defined by a generic matrix norm, called the Schatten norm, which includes most deterministic imperfect CSIT as special cases. Adopting worst-case robustness, the robust MIMO precoding design is formulated as a maximin problem to maximize the worst-case received signal-to-noise ratio or minimize the worst-case error probability. We show that the robust precoder admits a channel-diagonalizing structure for all Schatten norm based uncertainty sets, and then simplify the complex-valued matrix problem to a real-valued vector power allocation problem. We further show that the simplified power allocation problem can be analytically solved in a waterfilling manner, thus leading to a fully closed-form solution to the robust precoding design. Finally, we also investigate the robustness of beamforming and uniform-power transmission.