Re: [Qemu-devel] [PATCH 1/2] KVM: emulate lapic tsc deadline timer for guest

[Marcelo Tosatti]

On Thu, Sep 15, 2011 at 04:17:20PM +0800, Liu, Jinsong wrote:
> Marcelo Tosatti wrote:
> >> +  } else if (apic_lvtt_tscdeadline(apic)) {
> >> +          /* lapic timer in tsc deadline mode */
> >> +          u64 guest_tsc, guest_tsc_delta, ns = 0;
> >> +          struct kvm_vcpu *vcpu = apic->vcpu;
> >> +          unsigned long this_tsc_khz = vcpu_tsc_khz(vcpu); +              
> >> unsigned long
> >> flags; +
> >> +          if (unlikely(!apic->lapic_timer.tscdeadline || !this_tsc_khz))
> >> +                  return; +
> >> +          local_irq_save(flags);
> >> +
> >> +          now = apic->lapic_timer.timer.base->get_time();
> >> +          kvm_get_msr(vcpu, MSR_IA32_TSC, &guest_tsc);
> > 
> > Use kvm_x86_ops->read_l1_tsc(vcpu) instead of direct MSR read
> > (to avoid reading L2 guest TSC in case of nested virt).
> > 
> >> +          guest_tsc_delta = apic->lapic_timer.tscdeadline - guest_tsc;
> > 
> > if (guest_tsc <= tscdeadline), the timer should start immediately.
> > 
> 
> Yes, under such case the timer does start immediately, with ns = 0

No, guest_tsc_delta is unsigned, so the "< 0" comparation fails.