FHE-CGRA: Enable Efficient Acceleration of Fully Homomorphic Encryption on CGRAs

Fully Homomorphic Encryption (FHE) is an attractive privacy-preserving technique that allows computation directly on encrypted data without decryption. However, it incurs significant performance and memory costs due to intensive computations. In this work, we investigate the execution of FHE-enabled machine learning (ML) applications. We show that the runtime hardware reconfigurability of the underlying execution units of homomorphic operations is highly desirable for efficient hardware resource utilization during FHE-ML execution, due to the changing FHE encryption variants across different ML stages (e.g., the multiplicative level of the ciphertext) and corresponding optimal execution unit design. Based on the observation, we propose FHE-CGRA, a coarse-grained re-configurable architecture (CGRA) acceleration framework with an MLIR-based compiler toolchain for end-to-end homomorphic applications. The experiment shows that FHE-CGRA achieves up-to 8.15× speedup against a conventional CGRA baseline for accelerating the inference of FHE-encrypted convolution neural network (FHE-CNN) models, and up-to 16.48× power efficiency w.r.t. the state-of-the-art FPGA-based FHE-CNN accelerator design.