Resistive random-access memory (RRAM) provides an excellent platform for analog matrix computing (AMC), enabling both matrix-vector multiplication (MVM) and the solution of matrix equations through open-loop and closed-loop circuit architectures. While RRAM-based AMC has been widely explored for accelerating neural networks, its application to signal processing in massive multiple-input multiple-output (MIMO) wireless communication is rapidly emerging as a promising direction. In this Review, we summarize recent advances in applying AMC to massive MIMO, including DFT/IDFT computation for OFDM modulation and demodulation using MVM circuits; MIMO detection and precoding using MVM-based iterative algorithms; and rapid one-step solutions enabled by matrix inversion (INV) and generalized inverse (GINV) circuits. We also highlight additional opportunities, such as AMC-based compressed-sensing recovery for channel estimation and eigenvalue circuits for leakage-based precoding. Finally, we outline key challenges, including RRAM device reliability, analog circuit precision, array scalability, and data conversion bottlenecks, and discuss the opportunities for overcoming these barriers. With continued progress in device-circuit-algorithm co-design, RRAM-based AMC holds strong promise for delivering high-efficiency, high-reliability solutions to (ultra)massive MIMO signal processing in the 6G era.