Asahi Linux Works Around Missing PSCI on Apple Silicon

The latest Asahi Linux progress report details ongoing efforts to properly power-manage Apple Silicon CPU cores. Because Apple's chips lack an EL3 firmware layer, the kernel cannot use the standard PSCI interface via SMC or HVC calls, forcing the project to rely on a custom cpuidle driver that cannot be upstreamed. Developer Sven is now implementing a UEFI Runtime Services-based PSCI conduit, positioning m1n1 as a firmware layer the kernel can call back into for core power-state transitions, with kernel patches already posted to the mailing list as an RFC.

Separately, Apple's M4 series locks down the 'chicken bit' registers that previously allowed fine-grained control over state retention during WFI, causing crashes when a core unexpectedly loses its state. A new kernel command-line parameter, already merged into linux-next, works around this by making idle-loop behavior configurable during early boot.

The report also covers Apple's Secure Page Table Monitor (SPTM), which moves page-table management into the Guarded Execution Framework, evolving from the earlier Page Protection Layer to close off attack vectors that exploited PPL. Collectively, this work illustrates how the Asahi team is navigating between Linux's strict arm64 upstream requirements and Apple's nonstandard hardware, with direct implications for battery life and stability.