[RFC PATCH v3 17/21] KVM: x86: Avoid global clock update on setting KVM clock MSR

[David Woodhouse]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

Commit 0061d53daf26 ("KVM: x86: limit difference between kvmclock updates")
introduced a KVM_REQ_GLOBAL_CLOCK_UPDATE when one vCPU set up its clock.

This was a workaround for the ever-drifting clocks which were based on the
host's CLOCK_MONOTONIC and thus subject to NTP skew. On booting or resuming
a guest, it just leads to running kvm_guest_time_update() twice for each
vCPU for now good reason.

Just use KVM_REQ_CLOCK_UPDATE on the vCPU itself, and only in the case
where the KVM clock is being set up, not turned off.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 437412b36cae..32a873d5ed00 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2361,13 +2361,13 @@ static void kvm_write_system_time(struct kvm_vcpu *vcpu, gpa_t system_time,
 	}
 
 	vcpu->arch.time = system_time;
-	kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu);
 
 	/* we verify if the enable bit is set... */
-	if (system_time & 1)
+	if (system_time & 1) {
 		kvm_gpc_activate(&vcpu->arch.pv_time, system_time & ~1ULL,
 				 sizeof(struct pvclock_vcpu_time_info));
-	else
+		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
+	} else
 		kvm_gpc_deactivate(&vcpu->arch.pv_time);
 
 	return;
-- 
2.44.0