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

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Date:	Thu, 21 Jan 2016 05:46:50 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Yang Zhang <yang.zhang.wz@...il.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"rkrcmar@...hat.com" <rkrcmar@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver
 lowest-priority interrupts



> -----Original Message-----
> From: Yang Zhang [mailto:yang.zhang.wz@...il.com]
> Sent: Thursday, January 21, 2016 1:43 PM
> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
> rkrcmar@...hat.com
> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
> Subject: Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-
> priority interrupts
> 
> On 2016/1/21 13:33, Wu, Feng wrote:
> >
> >
> >> -----Original Message-----
> >> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> >> owner@...r.kernel.org] On Behalf Of Yang Zhang
> >> Sent: Thursday, January 21, 2016 1:24 PM
> >> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
> >> rkrcmar@...hat.com
> >> Cc: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
> >> 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@...el.com>
> >>> ---
> >>>    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?

I don't think there are problems, here we only cover lowest-priority mode.

Thanks,
Feng

> 
> --
> best regards
> yang