Re: [PATCH 0/4] arm64: Support the TSO memory model

[Zayd Qumsieh]

The patch looks great! :) I have one minor suggestion, though:

>static __always_inline bool system_has_actlr_state(void)
>{
>	return IS_ENABLED(CONFIG_ARM64_ACTLR_STATE) &&
>		alternative_has_cap_unlikely(ARM64_HAS_TSO_APPLE);
>}

ACTLR_EL1.TSO is not exposed for writing on Virtual Machines on all
versions of MacOS. However, AIDR_EL1 may still advertise TSO, whether
or not ACTLR_EL1.TSO is writable. Could you modify the patch such that
we check the writability of ACTLR_EL1.TSO in system_has_actlr_state
(or once on startup, and cache it, since reading from AIDR_EL1 causes
a trap to Hypervisor.fwk)?

Thanks,
Zayd