How guest code actually runs on a physical CPU: trap-and-emulate, binary translation, paravirtualization, and hardware-assisted virtualization (VT-x, AMD-V). Plus vCPU scheduling, gang scheduling, and the exit-cost story.
Memory consistency models define which reorderings are legal. A walk through SC, TSO (x86), PSO, and relaxed models (ARM / POWER), plus the memory barriers used to enforce ordering when it matters.
How multi-core CPUs keep a consistent view of memory — the MESI protocol, bus snooping, cache-to-cache transfers, and the store-buffer / invalid-queue optimizations (plus the memory-ordering headaches they introduce).