Cylon: Fast and Accurate Full-System Emulation of CXL-SSDs

We present Cylon, a fast and extensible full-system emulator for CXL-SSDs built on FEMU. Cylon bridges the gap between closed hardware prototypes and slow software simulators by faithfully reproducing sub-µs cache hits and tens-of-µs misses that fall to NAND through a hybrid execution path that mitigates hypervisor trap overheads. Cylon supports configurable caching policies and provides an applicationlevel interface for hardware-software co-design. Validated against a real CXL-SSD prototype, Cylon accurately models performance across a wide range of applications, from microbenchmarks to full-scale workloads. Our evaluation shows that Cylon reproduces realistic latency distributions, executes unmodified applications at near bare-metal speed, and scales to system-level studies. By combining speed, fidelity, and extensibility, Cylon fills a critical gap for evaluating today's CXL-SSDs and exploring next-generation architectures that blend CXL-enabled memory and storage semantics.