KVM: x86: Avoid periodic KVM clock updates in master clock mode

When the KVM clock is in master clock mode, updating the KVM clock is
pointless. Let the periodic work 'expire', and start it running again
from kvm_end_pvclock_update() if the master clock mode is ever turned
off again.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6913a6bd4126bec792a119588b4bfbe94f944d35..010394743885fc02b66bb70c79af4abe72e7a3ef 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -160,6 +160,8 @@ module_param(min_timer_period_us, uint, 0644);
 static bool __read_mostly kvmclock_periodic_sync = true;
 module_param(kvmclock_periodic_sync, bool, 0444);
 
+#define KVMCLOCK_SYNC_PERIOD (300 * HZ)
+
 /* tsc tolerance in parts per million - default to 1/2 of the NTP threshold */
 static u32 __read_mostly tsc_tolerance_ppm = 250;
 module_param(tsc_tolerance_ppm, uint, 0644);
@@ -3177,6 +3179,10 @@ static void kvm_end_pvclock_update(struct kvm *kvm)
        kvm_for_each_vcpu(i, vcpu, kvm)
                kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 
+       if (kvmclock_periodic_sync && !kvm->arch.use_master_clock)
+               schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
+                                     KVMCLOCK_SYNC_PERIOD);
+
        /* guest entries allowed */
        kvm_for_each_vcpu(i, vcpu, kvm)
                kvm_clear_request(KVM_REQ_MCLOCK_INPROGRESS, vcpu);
@@ -3545,8 +3551,6 @@ static void kvm_gen_kvmclock_update(struct kvm_vcpu *v)
                                        KVMCLOCK_UPDATE_DELAY);
 }
 
-#define KVMCLOCK_SYNC_PERIOD (300 * HZ)
-
 static void kvmclock_sync_fn(struct work_struct *work)
 {
        struct delayed_work *dwork = to_delayed_work(work);
@@ -3554,6 +3558,9 @@ static void kvmclock_sync_fn(struct work_struct *work)
                                           kvmclock_sync_work);
        struct kvm *kvm = container_of(ka, struct kvm, arch);
 
+       if (!kvm->arch.use_master_clock)
+               return;
+
        schedule_delayed_work(&kvm->arch.kvmclock_update_work, 0);
        schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
                                        KVMCLOCK_SYNC_PERIOD);
@@ -12551,7 +12558,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 
        mutex_unlock(&vcpu->mutex);
 
-       if (kvmclock_periodic_sync && vcpu->vcpu_idx == 0)
+       if (kvmclock_periodic_sync && !kvm->arch.use_master_clock &&
+           vcpu->vcpu_idx == 0)
                schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
                                                KVMCLOCK_SYNC_PERIOD);
 }