linux-kernel - [PATCH V2] x86/apic: Stop the TSC Deadline timer during lapic timer shutdown

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Message-Id: <20241009072001.509508-1-rui.zhang@intel.com>
Date: Wed,  9 Oct 2024 15:20:01 +0800
From: Zhang Rui <rui.zhang@...el.com>
To: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	rafael.j.wysocki@...el.com,
	x86@...nel.org,
	linux-pm@...r.kernel.org
Cc: hpa@...or.com,
	peterz@...radead.org,
	thorsten.blum@...lux.com,
	yuntao.wang@...ux.dev,
	tony.luck@...el.com,
	len.brown@...el.com,
	srinivas.pandruvada@...el.com,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH V2] x86/apic: Stop the TSC Deadline timer during lapic timer shutdown

This 12-year-old bug prevents some modern processors from achieving
maximum power savings during suspend. For example, Lunar Lake systems
gets 0% package C-states during suspend to idle and this causes energy
star compliance tests to fail.

According to Intel SDM, for the local APIC timer,
1. "The initial-count register is a read-write register. A write of 0 to
   the initial-count register effectively stops the local APIC timer, in
   both one-shot and periodic mode."
2. "In TSC deadline mode, writes to the initial-count register are
   ignored; and current-count register always reads 0. Instead, timer
   behavior is controlled using the IA32_TSC_DEADLINE MSR."
   "In TSC-deadline mode, writing 0 to the IA32_TSC_DEADLINE MSR disarms
   the local-APIC timer."

Stop the TSC Deadline timer in lapic_timer_shutdown() by writing 0 to
MSR_IA32_TSC_DEADLINE.

Cc: stable@...r.kernel.org
Fixes: 279f1461432c ("x86: apic: Use tsc deadline for oneshot when available")
Signed-off-by: Zhang Rui <rui.zhang@...el.com>
---
Changes since V1
- improve changelog
---
 arch/x86/kernel/apic/apic.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 6513c53c9459..d1006531729a 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -441,6 +441,10 @@ static int lapic_timer_shutdown(struct clock_event_device *evt)
 	v |= (APIC_LVT_MASKED | LOCAL_TIMER_VECTOR);
 	apic_write(APIC_LVTT, v);
 	apic_write(APIC_TMICT, 0);
+
+	if (boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER))
+		wrmsrl(MSR_IA32_TSC_DEADLINE, 0);
+
 	return 0;
 }

-- 
2.34.1