On Fri, 2026-07-24 at 14:19 -0700, Sean Christopherson wrote: > On Fri, Jul 03, 2026, David Woodhouse wrote: > > 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]> > > --- > > 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 ff45577ed90c..2039bd8518fb 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -13110,6 +13110,8 @@ 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) > > Any reason this can't be? > > if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu)) > kvm_update_masterclock(vcpu->kvm); > > > + kvm_update_masterclock(vcpu->kvm); > > I don't love doing work outside of KVM_RUN that is typically handled by > KVM_RUN, > but this seems fine?
I think I tried that first and it didn't work because KVM_REQ_MASTERCLOCK_UPDATE wasn't actually set yet. I remember going round in circles a few times here. I'll take another look.
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