Filesystem Encryption or Direct-Access for NVM Filesystems? Let's Have Both!

Emerging Non-Volatile Memories (NVMs) are promising candidates to build ultra-low idle power memory and storage devices in future computing systems. Unlike DRAM, NVMs do not require frequent refresh operations, and they can retain data after crashes and power loss. With such features, NVM memory modules can be used partly as a conventional memory to host memory pages and partly as file storage to host filesystems and persistent data. Most importantly, and unlike current storage technologies, NVMs can be directly attached to the memory bus and accessed through conventional load/store operations.As NVMs feature ultra-low access latency, it is necessary to minimize software overheads for accessing files to enable the full potential. In legacy storage devices, e.g., Flash and Harddisk drives, access latency dominates the software overheads. However, emerging NVMs’ performance can be burdened by the software overheads since memory access latency is minimal. Modern Operating Systems (OSes) allow direct-access (DAX) for NVM-hosted files through direct load/store operations by eliminating intermediate software layers. Unfortunately, we observe that such a direction ignores filesystem encryption and renders most of the current filesystem encryption implementations inapplicable to future NVM systems. In this paper, we propose a novel hardware/software co-design architecture that enables transparent filesystem encryption without sacrificing the direct-access feature of files in emerging NVMs with minimal change in OS and memory controller. Our proposed model incurs a negligible overall slowdown of 3.8% for workloads representative of real-world applications, while software-based encryption can incur as high as 5x slowdown for some applications.