On Fri, Feb 25, 2022, David Woodhouse wrote: > On Fri, 2022-02-25 at 01:39 +0000, Sean Christopherson wrote: > > @@ -11160,7 +11162,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu) > > vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT; > > kvm_vcpu_mtrr_init(vcpu); > > vcpu_load(vcpu); > > - kvm_set_tsc_khz(vcpu, max_tsc_khz); > > + kvm_set_tsc_khz(vcpu, max_tsc_khz ? : tsc_khz); > > kvm_vcpu_reset(vcpu, false); > > kvm_init_mmu(vcpu); > > vcpu_put(vcpu); > > > > Hm, now if you hit that race you end up potentially giving *different* > frequencies to different vCPUs in a single guest, depending on when > they were created. Yep. Though the race is much harder to hit (userspace vs TSC refinement). The existing race being hit is essentially do_initcalls() vs. TSC refinement. > How about this... (and as noted, I think I want to add an explicit KVM > ioctl to set kvm->arch.default_tsc_khz for subsequently created vCPUs). This wouldn't necessarily help. E.g. assuming userspace knows the actual TSC frequency, creating a vCPU before refinement completes might put the vCPU in "always catchup" purgatory. To really fix the race, KVM needs a notification that refinement completed (or failed). KVM could simply refuse to create vCPUs until it got the notification. In the non-constant case, KVM would also need to refresh max_tsc_khz.
