Asahi Linux 7.2: PSCI Over UEFI, M4 Idle Fixes, and SPTM Hypervisor Emulation

Asahi Linux's latest progress report for the 7.2 release is a dense mix of low-level hardware hacking and kernel engineering. The headline: the project is now implementing a PSCI conduit over UEFI Runtime Services, because Apple Silicon doesn't have EL3. That's a first for the ARM64 kernel ecosystem.

PSCI Without EL3

Apple's cores lack EL3, so the kernel can't use the standard SMC or HVC conduits to reach PSCI firmware. The arm64 maintainers require PSCI for power management, which blocks upstreaming Asahi's custom cpuidle driver. The project's solution: m1n1 reserves its memory and leaves behind a PSCI implementation that the kernel can call via UEFI Runtime Services. The spec lists SMC and HVC as examples, not requirements, so this is a legitimate reading. Patches are already on the mailing list as an RFC.

M4 Idle Crash Workaround

Starting with M4, Apple locks down the chicken bits that configure WFI state retention. The result: WFI on M4 loses core state and crashes. Yureka added a kernel command-line parameter to make idle loop behavior configurable, including a no-op loop that prevents crashes during early boot before the cpuidle driver takes over. The fix is already in linux-next.

SPTM Emulation in m1n1

Apple's Secure Page Table Monitor (SPTM) is mandatory for XNU on M4+, and it runs in a parallel exception level (GL2) with SPRR. That rendered the m1n1 hypervisor nonfunctional on M4. Sven's earlier reverse engineering of SPRR and GXF paid off: m1n1 now emulates both, letting it load Apple's SPTM blob, run XNU under the hypervisor, and trace MMIO as before. Tracing is slower, but it keeps hardware bring-up viable.

M3 Peripherals

Webcam and microphone support landed for all M3 series devices, with new initialization sequences for the ISP and a high-frequency decimator. ATCPHY (USB3/DP/Thunderbolt negotiation) also needed updated tunables for TSMC's N3 process.