MIPS: KVM: Migrate hrtimer to follow VCPU

When a VCPU is scheduled in on a different CPU, refresh the hrtimer used
for emulating count/compare so that it gets migrated to the same CPU.

This should prevent a timer interrupt occurring on a different CPU to
where the guest it relates to is running, which would cause the guest
timer interrupt not to be delivered until after the next guest exit.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: kvm@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: Sanjay Lal <sanjayl@kymasys.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/kvm/kvm_tlb.c

@@ -656,6 +656,23 @@ void kvm_local_flush_tlb_all(void)
 	local_irq_restore(flags);
 }
 
+/**
+ * kvm_mips_migrate_count() - Migrate timer.
+ * @vcpu:	Virtual CPU.
+ *
+ * Migrate CP0_Count hrtimer to the current CPU by cancelling and restarting it
+ * if it was running prior to being cancelled.
+ *
+ * Must be called when the VCPU is migrated to a different CPU to ensure that
+ * timer expiry during guest execution interrupts the guest and causes the
+ * interrupt to be delivered in a timely manner.
+ */
+static void kvm_mips_migrate_count(struct kvm_vcpu *vcpu)
+{
+	if (hrtimer_cancel(&vcpu->arch.comparecount_timer))
+		hrtimer_restart(&vcpu->arch.comparecount_timer);
+}
+
 /* Restore ASID once we are scheduled back after preemption */
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
@@ -691,6 +708,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (vcpu->arch.last_sched_cpu != cpu) {
 		kvm_info("[%d->%d]KVM VCPU[%d] switch\n",
 			 vcpu->arch.last_sched_cpu, cpu, vcpu->vcpu_id);
+		/*
+		 * Migrate the timer interrupt to the current CPU so that it
+		 * always interrupts the guest and synchronously triggers a
+		 * guest timer interrupt.
+		 */
+		kvm_mips_migrate_count(vcpu);
 	}
 
 	if (!newasid) {