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Date: Thu, 15 Sep 2011 08:45:31 -0300
From: Marcelo Tosatti <mtosatti@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] KVM: emulate lapic tsc deadline timer
	for guest
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To: "Liu, Jinsong" <jinsong.liu@intel.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>, Avi Kivity <avi@redhat.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

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.