Re: [PATCH RFC V6 1/5] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

[Gleb Natapov <gleb@redhat.com>]

On Sun, Apr 29, 2012 at 04:18:03PM +0300, Avi Kivity wrote:
> On 04/24/2012 12:59 PM, Gleb Natapov wrote:
> > >  
> > > +/*
> > > + * kvm_pv_kick_cpu_op:  Kick a vcpu.
> > > + *
> > > + * @apicid - apicid of vcpu to be kicked.
> > > + */
> > > +static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
> > > +{
> > > +	struct kvm_vcpu *vcpu = NULL;
> > > +	int i;
> > > +
> > > +	kvm_for_each_vcpu(i, vcpu, kvm) {
> > > +		if (!kvm_apic_present(vcpu))
> > > +			continue;
> > > +
> > > +		if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
> > > +			break;
> > > +	}
> > > +	if (vcpu) {
> > > +		/*
> > > +		 * Setting unhalt flag here can result in spurious runnable
> > > +		 * state when unhalt reset does not happen in vcpu_block.
> > > +		 * But that is harmless since that should soon result in halt.
> > > +		 */
> > > +		vcpu->arch.pv.pv_unhalted = 1;
> > > +		/* We need everybody see unhalt before vcpu unblocks */
> > > +		smp_mb();
> > > +		kvm_vcpu_kick(vcpu);
> > > +	}
> > > +}
> > This is too similar to kvm_irq_delivery_to_apic(). Why not reuse it. We
> > can use one of reserved delivery modes as PV delivery mode. We will
> > disallow guest to trigger it through apic interface, so this will not be
> > part of ABI and can be changed at will.
> >
> 
> I'm not thrilled about this.  Those delivery modes will eventually
> become unreserved.  We can have a kvm_lookup_apic_id() that is shared
> among implementations.
> 
This is only internal implementation. If they become unreserved we will
use something else.

--
			Gleb.