[patch 14/16] KVM: x86: notifier for clocksource changes

[Marcelo Tosatti <mtosatti@redhat.com>]

[-- Attachment #1: 15-add-kvm-req-pvclock-gtod-update --]
[-- Type: text/plain, Size: 2592 bytes --]

Register a notifier for clocksource change event. In case
the host switches to clock other than TSC, disable master
clock usage.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: vsyscall/arch/x86/kvm/x86.c
===================================================================
--- vsyscall.orig/arch/x86/kvm/x86.c
+++ vsyscall/arch/x86/kvm/x86.c
@@ -1218,6 +1218,7 @@ static bool kvm_get_time_and_clockread(s
 	return true;
 }
 
+static atomic_t kvm_guest_has_master_clock = ATOMIC_INIT(0);
 
 /*
  *
@@ -1271,6 +1272,8 @@ static void pvclock_update_vm_gtod_copy(
 	ka->use_master_clock = kvm_get_time_and_clockread(
 					&ka->master_kernel_ns,
 					&ka->master_cycle_now);
+	if (ka->use_master_clock)
+		atomic_set(&kvm_guest_has_master_clock, 1);
 
 	vclock_mode = pvclock_gtod_data.clock.vclock_mode;
 	trace_kvm_update_master_clock(ka->use_master_clock, vclock_mode);
@@ -5124,6 +5127,44 @@ static void kvm_set_mmio_spte_mask(void)
 	kvm_mmu_set_mmio_spte_mask(mask);
 }
 
+static void pvclock_gtod_update_fn(struct work_struct *work)
+{
+	struct kvm *kvm;
+	struct kvm_vcpu *vcpu;
+	int i;
+
+	raw_spin_lock(&kvm_lock);
+	list_for_each_entry(kvm, &vm_list, vm_list)
+		kvm_for_each_vcpu(i, vcpu, kvm)
+			set_bit(KVM_REQ_MASTERCLOCK_UPDATE, &vcpu->requests);
+	atomic_set(&kvm_guest_has_master_clock, 0);
+	raw_spin_unlock(&kvm_lock);
+}
+
+static DECLARE_WORK(pvclock_gtod_work, pvclock_gtod_update_fn);
+
+/*
+ * Notification about pvclock gtod data update.
+ */
+static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused,
+			       void *unused2)
+{
+	struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
+
+	/* disable master clock if host does not trust, or does not
+ 	 * use, TSC clocksource
+ 	 */
+	if (gtod->clock.vclock_mode != VCLOCK_TSC &&
+	    atomic_read(&kvm_guest_has_master_clock) != 0)
+		queue_work(system_long_wq, &pvclock_gtod_work);
+
+	return 0;
+}
+
+static struct notifier_block pvclock_gtod_notifier = {
+	.notifier_call = pvclock_gtod_notify,
+};
+
 int kvm_arch_init(void *opaque)
 {
 	int r;
@@ -5165,6 +5206,8 @@ int kvm_arch_init(void *opaque)
 		host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
 
 	kvm_lapic_init();
+	pvclock_gtod_register_notifier(&pvclock_gtod_notifier);
+
 	return 0;
 
 out:
@@ -5179,6 +5222,7 @@ void kvm_arch_exit(void)
 		cpufreq_unregister_notifier(&kvmclock_cpufreq_notifier_block,
 					    CPUFREQ_TRANSITION_NOTIFIER);
 	unregister_hotcpu_notifier(&kvmclock_cpu_notifier_block);
+	pvclock_gtod_unregister_notifier(&pvclock_gtod_notifier);
 	kvm_x86_ops = NULL;
 	kvm_mmu_module_exit();
 }