Re: [PATCH v2] KVM: x86: reset lapic_timer.expired_tscdeadline at SET_LAPIC time

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Jun 21, 2016 at 09:50:54AM +0200, Paolo Bonzini wrote:
> 
> 
> On 20/06/2016 15:05, Marcelo Tosatti wrote:
> > 
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ea306ad..89be6e9 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2991,6 +2991,7 @@ static int kvm_vcpu_ioctl_set_lapic(struct kvm_vcpu *vcpu,
> >  {
> >  	kvm_apic_post_state_restore(vcpu, s);
> >  	update_cr8_intercept(vcpu);
> > +	vcpu->arch.apic->lapic_timer.expired_tscdeadline = 0;
> >  
> 
> I think this is not correct.  You have programmed the host timer to an
> early value when kvm_apic_post_state_restore called start_apic_timer.
> 
> I think that:
> 
> 1) post_state_restore should cancel the timer and clear
> lapic_timer.pending before writing the registers, not afterwards.
> lapic_timer.expired_tscdeadline can be cleared at the same time.
> 
> 2) kvm_write_tsc should do the same and restart the timer afterwards.
> 
> Thanks,
> 
> Paolo

Actually, the max should deal with the problem Alan is having with
vmload as well (one delay of tenths of microseconds, or 0, per vmload
should be irrelevant).