Re: [PATCH v3 04/12] KVM: X86: Add a ratio parameter to kvm_scale_tsc()

Sean Christopherson
2021-05-24T16:10:27Z

On Mon, May 24, 2021, Paolo Bonzini wrote:
> On 21/05/21 12:24, Ilias Stamatis wrote:
> > @@ -3537,10 +3539,14 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > * return L1's TSC value to ensure backwards-compatible
> > * behavior for migration.
> > */
> > - u64 tsc_offset = msr_info->host_initiated ? vcpu->arch.l1_tsc_offset :
> > - vcpu->arch.tsc_offset;
> > -
> > - msr_info->data = kvm_scale_tsc(vcpu, rdtsc()) + tsc_offset;
> > + if (msr_info->host_initiated)
> > + msr_info->data = kvm_scale_tsc(
> > + vcpu, rdtsc(), vcpu->arch.l1_tsc_scaling_ratio
> > + ) + vcpu->arch.l1_tsc_offset;
>
> Better indentation:
>
> msr_info->data = vcpu->arch.l1_tsc_offset +
> kvm_scale_tsc(vcpu, rdtsc(),

I like this more, but it's still a bit ugly.

> vcpu->arch.tsc_scaling_ratio);

Wrong pairing of ratio and offset (not necessarily what you queued, obviously).

>
> Same below.

Alternatively, what about something like this?

u64 offset, ratio;

if (msr_info->host_initiated) {
offset = vcpu->arch.l1_tsc_offset;
ratio = vcpu->arch.l1_tsc_scaling_ratio;
} else {
offset = vcpu->arch.tsc_offset;
ratio = vcpu->arch.tsc_scaling_ratio;
}
msr_info->data = kvm_scale_tsc(vcpu, rdtsc(), ratio) + offset;

or an option that would require additional refactoring:

struct kvm_guest_tsc *tsc;

tsc = msr_info->host_initiated ? &vcpu->arch.l1_tsc :
&vcpu->arch.current_tsc;

msr_info->data = tsc->offset +
kvm_scale_tsc(vcpu, rdtsc(), tsc->scaling_ratio);

>
> Paolo
>
> > + else
> > + msr_info->data = kvm_scale_tsc(
> > + vcpu, rdtsc(), vcpu->arch.tsc_scaling_ratio
> > + ) + vcpu->arch.tsc_offset;
> > break;
> > }
> > case MSR_MTRRcap:
> >
>