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

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Message-id: <20240416021100.87652-1-zayd_qumsieh@apple.com>
Date: Mon, 15 Apr 2024 19:11:00 -0700
From: Zayd Qumsieh <zayd_qumsieh@...le.com>
To: marcan@...can.st
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Subject: Re: [PATCH 0/4] arm64: Support the TSO memory model

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