linux-kernel - Re: [PATCH v2 11/13] KVM: x86: add KVM_CAP_X2APIC

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Date:	Mon, 11 Jul 2016 12:40:02 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Yang Zhang <yang.zhang.wz@...il.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:	"Lan, Tianyu" <tianyu.lan@...el.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Jan Kiszka <jan.kiszka@....de>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v2 11/13] KVM: x86: add KVM_CAP_X2APIC_API



On 11/07/2016 12:33, Yang Zhang wrote:
> On 2016/7/11 17:17, Paolo Bonzini wrote:
>> On 11/07/2016 10:56, Yang Zhang wrote:
>>> On 2016/7/11 15:44, Paolo Bonzini wrote:
>>>> On 11/07/2016 08:06, Yang Zhang wrote:
>>>> If interrupt remapping is on, KVM_CAP_X2APIC_API is needed even with 8
>>>> VCPUs, I think.  Otherwise KVM will believe that 0xff is "broadcast"
>>>> rather than "cluster 0, CPUs 0-7".
>>>
>>> If interrupt remapping is using, what 0xff means is relying on which
>>> mode the destination CPU is in. I think there is no KVM_CAP_X2APIC_API
>>> needed since interrupt remapping table gives all the information.
>>
>> If you have EIM 0xff never means broadcast, but KVM sees a 0xff in the
>> interrupt route or KVM_SIGNAL_MSI argument and translates it into a
>> broadcast.
> 
> I see your point. I thought there would be a new irq router(like
> KVM_IRQ_ROUTING_IR) to handle all interrupts after turn on IR and
> KVM_CAP_X2APIC_API would be dropped.

KVM_CAP_X2APIC_API seems simpler to me than a new type of irq routing.

> So we will continue to use
> KVM_IRQ_ROUTING_IRQCHIP and KVM_IRQ_ROUTING_MSI for interrupt from IR,
> right?

Actually only KVM_IRQ_ROUTING_MSI, because that's the only one that is
available with split irqchip.

Paolo