KVM: Move apic timer migration away from critical section

Migrating the apic timer in the critical section is not very nice, and is
absolutely horrible with the real-time port.  Move migration to the regular
vcpu execution path, triggered by a new bitflag.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/irq.h

@@ -83,6 +83,6 @@ void kvm_pic_reset(struct kvm_kpic_state *s);
 void kvm_timer_intr_post(struct kvm_vcpu *vcpu, int vec);
 void kvm_inject_pending_timer_irqs(struct kvm_vcpu *vcpu);
 void kvm_inject_apic_timer_irqs(struct kvm_vcpu *vcpu);
-void kvm_migrate_apic_timer(struct kvm_vcpu *vcpu);
+void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu);
 
 #endif

arch/x86/kvm/lapic.c

@@ -1092,7 +1092,7 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu)
 	start_apic_timer(apic);
 }
 
-void kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
+void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct hrtimer *timer;
@@ -1104,7 +1104,6 @@ void kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
 	if (hrtimer_cancel(timer))
 		hrtimer_start(timer, timer->expires, HRTIMER_MODE_ABS);
 }
-EXPORT_SYMBOL_GPL(kvm_migrate_apic_timer);
 
 void kvm_lapic_sync_from_vapic(struct kvm_vcpu *vcpu)
 {

arch/x86/kvm/x86.c

@@ -2518,13 +2518,16 @@ again:
 	if (unlikely(r))
 		goto out;
 
-	if (vcpu->requests)
+	if (vcpu->requests) {
+		if (test_and_clear_bit(KVM_REQ_MIGRATE_TIMER, &vcpu->requests))
+			__kvm_migrate_apic_timer(vcpu);
 		if (test_and_clear_bit(KVM_REQ_REPORT_TPR_ACCESS,
 				       &vcpu->requests)) {
 			kvm_run->exit_reason = KVM_EXIT_TPR_ACCESS;
 			r = 0;
 			goto out;
 		}
+	}
 
 	kvm_inject_pending_timer_irqs(vcpu);
 

include/linux/kvm_host.h

@@ -35,6 +35,7 @@
  * vcpu->requests bit members
  */
 #define KVM_REQ_TLB_FLUSH          0
+#define KVM_REQ_MIGRATE_TIMER      1
 #define KVM_REQ_REPORT_TPR_ACCESS  2
 
 struct kvm_vcpu;
@@ -277,6 +278,11 @@ static inline gpa_t gfn_to_gpa(gfn_t gfn)
 	return (gpa_t)gfn << PAGE_SHIFT;
 }
 
+static inline void kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
+{
+	set_bit(KVM_REQ_MIGRATE_TIMER, &vcpu->requests);
+}
+
 enum kvm_stat_kind {
 	KVM_STAT_VM,
 	KVM_STAT_VCPU,