[PATCH v6 43/51] 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.

Reviewed-by: David Woodhouse <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
 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 61d4d943fe74..41aff709b90a 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -152,7 +152,17 @@ 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)
@@ -223,6 +233,8 @@ 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)
@@ -318,6 +330,15 @@ static __init void kvm_sched_clock_init(bool 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);
 
-- 
2.55.0.679.g6767b8d81c-goog