[PATCH v8 04/17] KVM: x86: Activate master clock immediately on vCPU creation

From: David Woodhouse <[email protected]>

Previously, the master clock was only activated when the first vCPU
processed KVM_REQ_MASTERCLOCK_UPDATE during KVM_RUN. This meant that
KVM_GET_CLOCK could not return the host_tsc field until after the
first KVM_RUN, making it impossible for userspace to follow the
documented TSC migration procedure without a dummy vCPU run.

Fix this by calling kvm_update_masterclock() directly from
kvm_arch_vcpu_postcreate(), after kvm_synchronize_tsc() has already
set all_vcpus_matched_freq. This ensures the master clock is active
immediately, and KVM_GET_CLOCK returns a valid {host_tsc, realtime}
pair as soon as a vCPU exists.

Signed-off-by: David Woodhouse <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
 arch/x86/kvm/x86.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ce6d155b2ee6..3ebcf2f27f7d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9447,6 +9447,8 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
 		return;
 	vcpu_load(vcpu);
 	kvm_synchronize_tsc(vcpu, NULL);
+	if (!vcpu->kvm->arch.use_master_clock)
+		kvm_update_masterclock(vcpu->kvm);
 	vcpu_put(vcpu);
 
 	/* poll control enabled by default */
-- 
2.55.0.571.g244d577d93-goog