Context-Sensitive Decoding: On-Demand Microcode Customization for Security and Energy Management

Modern instruction set decoders feature translation of native instructions into internal micro-ops to simplify the CPU design and improve instruction-level parallelism. However, this translation is static in most known instances. This paper proposes context-sensitive decoding, a technique that enables customization of the micro-op translation based on the current execution context and/or preset hardware events. Further, it can transition between different translation modes rapidly. While there are many potential applications, this paper demonstrates its effectiveness with two use cases: 1) as a novel security defense to thwart instruction/data cache-based side-channel attacks; and 2) as a power management technique that performs selective devectorization to enable efficient unit-level power gating.