Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

[Yang Zhang]

On 2016/1/21 13:33, Wu, Feng wrote:
> > -----Original Message-----
> > From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Yang Zhang
> > Sent: Thursday, January 21, 2016 1:24 PM
> > To: Wu, Feng <feng.wu@xxxxxxxxx>; pbonzini@xxxxxxxxxx;
> > rkrcmar@xxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-
> > priority interrupts
> >
> > On 2016/1/20 9:42, Feng Wu wrote:
> > > Use vector-hashing to deliver lowest-priority interrupts, As an
> > > example, modern Intel CPUs in server platform use this method to
> > > handle lowest-priority interrupts.
> > >
> > > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > > ---
> > >    bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic
> > *src,
> > >    		struct kvm_lapic_irq *irq, int *r, unsigned long *dest_map)
> > >    {
> > > @@ -727,21 +743,51 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm
> > *kvm, struct kvm_lapic *src,
> > >    		dst = map->logical_map[cid];
> > >
> > > -		if (kvm_lowest_prio_delivery(irq)) {
> > > +		if (!kvm_lowest_prio_delivery(irq))
> > > +			goto set_irq;
> > > +
> > > +		if (!kvm_vector_hashing_enabled()) {
> > >    			int l = -1;
> > >    			for_each_set_bit(i, &bitmap, 16) {
> > >    				if (!dst[i])
> > >    					continue;
> > >    				if (l < 0)
> > >    					l = i;
> > > -				else if (kvm_apic_compare_prio(dst[i]->vcpu,
> > dst[l]->vcpu) < 0)
> > > +				else if (kvm_apic_compare_prio(dst[i]->vcpu,
> > > +							dst[l]->vcpu) < 0)
> > >    					l = i;
> > >    			}
> > > -
> > >    			bitmap = (l >= 0) ? 1 << l : 0;
> > > +		} else {
> > > +			int idx = 0;
> > > +			unsigned int dest_vcpus = 0;
> > > +
> > > +			dest_vcpus = hweight16(bitmap);
> > > +			if (dest_vcpus == 0)
> > > +				goto out;
> > > +
> > > +			idx = kvm_vector_2_index(irq->vector,
> > > +				dest_vcpus, &bitmap, 16);
> > > +
> > > +			/*
> > > +			 * We may find a hardware disabled LAPIC here, if
> > that
> > > +			 * is the case, print out a error message once for each
> > > +			 * guest and return.
> > > +			 */
> > > +			if (!dst[idx-1] &&
> > > +				(kvm->arch.disabled_lapic_found == 0)) {
> > > +				kvm->arch.disabled_lapic_found = 1;
> > > +				printk(KERN_ERR
> > > +					"Disabled LAPIC found during irq
> > injection\n");
> > > +				goto out;
> >
> > What does "goto out" mean? Inject successfully or fail? According the
> > value of ret which is set to ture here, it means inject successfully but
> > i = -1.
>
> Oh, I didn't notice 'ret' is initialized to true, I thought it was initialized
> to false like another function, I should add a "ret = false' here. We should
> failed to inject the interrupt since hardware disabled LAPIC is found.

I remember we have discussed that even the LAPIC is software disabled, 
it still can respond to some interrupts like INIT, NMI, SMI, and SIPI 
messages. Isn't current logic still problematically?

--
best regards
yang