linux-kernel - [PATCH v2 25/38] x86/kvmclock: Hook clocksource.suspend/resume when kvmclock isn't sched

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Message-ID: <20250227021855.3257188-26-seanjc@google.com>
Date: Wed, 26 Feb 2025 18:18:41 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Sean Christopherson <seanjc@...gle.com>, Juergen Gross <jgross@...e.com>, 
	"K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Ajay Kaher <ajay.kaher@...adcom.com>, 
	Jan Kiszka <jan.kiszka@...mens.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	John Stultz <jstultz@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, 
	kvm@...r.kernel.org, virtualization@...ts.linux.dev, 
	linux-hyperv@...r.kernel.org, xen-devel@...ts.xenproject.org, 
	Tom Lendacky <thomas.lendacky@....com>, Nikunj A Dadhania <nikunj@....com>
Subject: [PATCH v2 25/38] x86/kvmclock: Hook clocksource.suspend/resume when
 kvmclock isn't sched_clock

Save/restore kvmclock across suspend/resume via clocksource hooks when
kvmclock isn't being used for sched_clock.  This will allow using kvmclock
as a clocksource (or for wallclock!) without also using it for sched_clock.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kernel/kvmclock.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 0580fe1aefa0..319f8b2d0702 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -130,7 +130,17 @@ static void kvm_setup_secondary_clock(void)
 
 static void kvm_restore_sched_clock_state(void)
 {
-	kvm_register_clock("primary cpu clock, resume");
+	kvm_register_clock("primary cpu, sched_clock resume");
+}
+
+static void kvmclock_suspend(struct clocksource *cs)
+{
+	kvmclock_disable();
+}
+
+static void kvmclock_resume(struct clocksource *cs)
+{
+	kvm_register_clock("primary cpu, clocksource resume");
 }
 
 void kvmclock_cpu_action(enum kvm_guest_cpu_action action)
@@ -201,6 +211,8 @@ static struct clocksource kvm_clock = {
 	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
 	.id     = CSID_X86_KVM_CLK,
 	.enable	= kvm_cs_enable,
+	.suspend = kvmclock_suspend,
+	.resume = kvmclock_resume,
 };
 
 static void __init kvmclock_init_mem(void)
@@ -295,6 +307,15 @@ static void __init kvm_sched_clock_init(bool stable)
 	__paravirt_set_sched_clock(kvm_sched_clock_read, stable,
 				   kvm_save_sched_clock_state, kvm_restore_sched_clock_state);
 
+	/*
+	 * The BSP's clock is managed via dedicated sched_clock save/restore
+	 * hooks when kvmclock is used as sched_clock, as sched_clock needs to
+	 * be kept alive until the very end of suspend entry, and restored as
+	 * quickly as possible after resume.
+	 */
+	kvm_clock.suspend = NULL;
+	kvm_clock.resume = NULL;
+
 	pr_info("kvm-clock: using sched offset of %llu cycles",
 		kvm_sched_clock_offset);
 
-- 
2.48.1.711.g2feabab25a-goog