Re: [PATCH 3/4] KVM host implementation

[Peter Zijlstra]

On Tue, Aug 31, 2021 at 09:59:18AM +0800, Tianqiang Xu wrote:
> @@ -4304,8 +4374,14 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>  	idx = srcu_read_lock(&vcpu->kvm->srcu);
>  	if (kvm_xen_msr_enabled(vcpu->kvm))
>  		kvm_xen_runstate_set_preempted(vcpu);
> -	else
> +	else {
>  		kvm_steal_time_set_preempted(vcpu);
> +
> +		if (get_cpu_nr_running(smp_processor_id()) <= 1)
> +			kvm_steal_time_set_is_idle(vcpu);
> +		else
> +			kvm_steal_time_clear_is_idle(vcpu);
> +	}
>  	srcu_read_unlock(&vcpu->kvm->srcu, idx);


This cannot be right. The CPU could long since be running tasks again,
but as long as this vCPU crud doesn't run, the guest keeps thinking it's
physically idle.