Counter Advance for Reliable Encryption in Phase Change Memory

The use of hardware encryption and new memory technologies such as phase change memory (PCM) are gaining popularity in a variety of server applications such as cloud systems. While PCM provides energy and density advantages over conventional DRAM memory, it faces endurance challenges. Such challenges are exacerbated when employing memory encryption as the stored data is essentially randomized, losing data locality and reducing or eliminating the effectiveness of energy and endurance aware encoding techniques. This results in increasing dynamic energy consumption and accelerated wear out. In this paper we propose
counter advance
, a technique to leverage the process of encryption to improve reliability and lifetime while maintaining low-energy and low-latency operation. Counter advance is compatible with standard error-correction codes (ECC) and error correction pointers (ECP), the standard for mitigating endurance faults in PCM. Counter advance achieves the same fault tolerance using three ECP pointers for a
$10^{-4}$
cell failure rate compared to the leading approach to consider energy savings and reliability for encrypted PCM (SECRET) using five ECP pointers. At a failure rate of
$10^{-2}$
, counter advance can achieve an uncorrectable bit error rate (UBER) of 10
$^{-10}$
, compared to
${<}10^{-4}$
for SECRET, using six ECP pointers. This leads to a lifetime improvement of 3.8× while maintaining comparable energy consumption and access latency.