linux-kernel - Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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Message-ID: <20241112150809.GK6497@noisy.programming.kicks-ass.net>
Date: Tue, 12 Nov 2024 16:08:09 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: artem.bityutskiy@...ux.intel.com,
	Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	rafael.j.wysocki@...el.com, len.brown@...el.com,
	dave.hansen@...ux.intel.com
Subject: Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer
 cpuidle_play_dead() over mwait_play_dead()

On Tue, Nov 12, 2024 at 03:56:22PM +0100, Rafael J. Wysocki wrote:

> > So given we don't have any such code, why can't we simply fix the cstate
> > parsing we have in mwait_play_dead() and call it a day?
> 
> I'll leave this one to Artem, but there is at least one reason to
> avoid doing that I know about: There is no guarantee that whatever has
> been found was actually validated.

It's a bit daft to explicitly advertise a state in CPUID that's not
validated. I realize that MSFT will likely only ever use the ACPI table,
but at the same time, the CPUID bits and ACPI tables both come from the
same BIOS image, no?

.... and we've never seen the BIOS be self contradictory before ... /me
runs