Improving PCM Endurance with Randomized Address Remapping in Hybrid Memory System

Phase-Change-Memory (PCM) has emerged as a promising alternative of DRAM main memory. A new hybrid memory architecture, where DRAM serves as cache of PCM main memory, has been proposed to leverage PCM's high scalability and DRAM's fast access time. One biggest issue of PCM is the limited number of writes to storage cells. We argue that good cache mechanism will decrease PCM writes dramatically in hybrid memory system. In this paper, we demonstrate that traditional set associative cache is susceptible to malicious attacks, which lead certain PCM cells to wear-out by constant cache flushes. A novel approach called Randomized Address Remapping (RAR) is proposed to hide the mapping details between DRAM and PCM. With this approach, the attacks based on set associative cache do not work, while the efficiency of caching still remains. We present Static Randomized Address Remapping (SRAR) and Dynamic Randomized Address Remapping (DRAR) in this paper. SRAR invalidates set associative cache based attacks by distributing their address accesses to different sets. DRAR uses a region-based approach to change the mapping dynamically, in case that the static mapping relationship is discovered by attacker compromising operating system. Experimental results show that RAR approaches can prevent malicious attacks and improve PCM endurance greatly.