RCP: A Low-overhead Reversible Coherence Protocol

Abstract

This paper proposes RCP, a new reversible coherence protocol that ensures invisible speculative load execution (ISLE) with low overhead. RCP can be combined with processor mechanisms that eliminate the effects of speculative instructions on other instructions to achieve low overhead invisible speculative execution (ISE). ISE provides protection that is at least as strong as speculative privacy tracking (SPT) and stronger than speculative taint tracking (STT). RCP is designed by systematically extending the existing coherence protocol to incorporate speculative loads and states. The protocol is implemented in Gem5 and verified with Murphi. The results show that RCP based ISE incurs lower overhead than STT/SDO/SPT while providing similar/stronger protection.