linux-kernel - [RFC PATCH v4 5/8] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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Message-ID: <20241125132029.7241-6-patryk.wlazlyn@linux.intel.com>
Date: Mon, 25 Nov 2024 14:20:25 +0100
From: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	rafael.j.wysocki@...el.com,
	len.brown@...el.com,
	artem.bityutskiy@...ux.intel.com,
	dave.hansen@...ux.intel.com,
	patryk.wlazlyn@...ux.intel.com,
	peterz@...radead.org,
	tglx@...utronix.de,
	gautham.shenoy@....com
Subject: [RFC PATCH v4 5/8] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play_dead()

The algorithm based on cpuid leaf 0x5 in the mwait_play_dead(),
for looking up the mwait hint for the deepest cstate may calculate the
wrong hint on recent Intel x86 platforms.

Prefer cpuidle_play_dead() over the generic mwait_play_dead() loop and
only fallback to the later in case of missing appropriate enter_dead()
handler.

Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
---
 arch/x86/kernel/smpboot.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index d0464c7a0af5..2627b56fb9bc 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1413,9 +1413,10 @@ void native_play_dead(void)
 	play_dead_common();
 	tboot_shutdown(TB_SHUTDOWN_WFS);
 
+	/* The first successful play_dead() will not return */
+	cpuidle_play_dead();
 	mwait_play_dead();
-	if (cpuidle_play_dead())
-		hlt_play_dead();
+	hlt_play_dead();
 }
 
 #else /* ... !CONFIG_HOTPLUG_CPU */
-- 
2.47.0