On Mon, Jan 20, 2025, Vitaly Kuznetsov wrote: > Sean Christopherson <seanjc@xxxxxxxxxx> writes: > > > When updating paravirtual clocks, setup the Hyper-V TSC page before > > Xen PV clocks. This will allow dropping xen_pvclock_tsc_unstable in favor > > of simply clearing PVCLOCK_TSC_STABLE_BIT in the reference flags. > > > > Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > --- > > arch/x86/kvm/x86.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 9eabd70891dd..c68e7f7ba69d 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -3280,6 +3280,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) > > hv_clock.flags &= ~PVCLOCK_GUEST_STOPPED; > > } > > > > + kvm_hv_setup_tsc_page(v->kvm, &hv_clock); > > + > > #ifdef CONFIG_KVM_XEN > > if (vcpu->xen.vcpu_info_cache.active) > > kvm_setup_guest_pvclock(&hv_clock, v, &vcpu->xen.vcpu_info_cache, > > @@ -3289,7 +3291,6 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) > > kvm_setup_guest_pvclock(&hv_clock, v, &vcpu->xen.vcpu_time_info_cache, 0, > > xen_pvclock_tsc_unstable); > > #endif > > - kvm_hv_setup_tsc_page(v->kvm, &hv_clock); > > return 0; > > } > > "No functional change detected". > > Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > > (What I'm wondering is if (from mostly theoretical PoV) it's OK to pass > *some* of the PV clocks as stable and some as unstable to the same > guest, i.e. if it would make sense to disable Hyper-V TSC page when > KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE too. I think it's ok to keep the Hyper-V TSC page in this case. It's not that the Xen PV clock is truly unstable, it's that some guests get tripped up by the STABLE flag. A guest that can't handle the STABLE flag has bigger problems than the existence of a completely unrelated clock that is implied to be stable. > I don't know if anyone combines Xen and Hyper-V emulation capabilities for > the same guest on KVM though.) That someone would have to be quite "brave" :-D
