Fast and Efficient Secure L1 Caches for SMT.

Secure randomized caches use the latency budgets of last-level caches to isolate data by security domain. In contrast, L1 caches are very latency- and size-constrained (by cache ways and page size), hindering both the adoption of secure randomized designs and increases in size without losing backward compatibility due to page size changes. We propose a new secure and larger L1 cache design for SMT cores: SMTCache. SMTCache uses separate, identical L1 caches (slices) to isolate security domains. The overall cache size scales with the number of SMT threads, with individual slices mirroring current designs without changing the page size. SMTCache consumes less power than larger sets and does not increase hit latency. We show that SMTCache is a principled mitigation against L1 cache attacks and fundamentally precludes vulnerabilities like L1TF. Further, we measure that SMTCache improves L1 cache performance compared to current designs and even remains competitive with larger caches. For instance, on a system with SMT-2, SMTCache provides equivalent hit ratios across the SPEC CPU2017 suite to a state-of-the-art L1 cache of comparable size while improving system security and significantly reducing energy costs.