linux-kernel - Re: [PATCH v8 03/13] KVM: Define a new interface kvm_intr_is_single

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Date:	Thu, 17 Sep 2015 18:00:21 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	"Wu, Feng" <feng.wu@...el.com>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"joro@...tes.org" <joro@...tes.org>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 03/13] KVM: Define a new interface
 kvm_intr_is_single_vcpu()



On 17/09/2015 17:58, Radim Krčmář wrote:
> For interrupts from MSI and IOxAPIC:
> - Flat logical interrupts are delivered as if we had natural
>   (CPU0<->bit0, CPU1<->bit1, ...) flat logical xAPIC for first 8 VCPUs.
> - Cluster logical doesn't work much, it's interpreted like flat logical.
>   I didn't care about xAPIC cluster because Linux, the sole user of our
>   paravirtualized x2APIC, doesn't configure it.
> 
> I'll paste kvm_apic_mda() source for better explanation:
> 
>   static u32 kvm_apic_mda(unsigned int dest_id, struct kvm_lapic *source,
>                                                 struct kvm_lapic *target)
>   {
>   	bool ipi = source != NULL;
>   	bool x2apic_mda = apic_x2apic_mode(ipi ? source : target);
>   
>   	if (!ipi && dest_id == APIC_BROADCAST && x2apic_mda)
>   		return X2APIC_BROADCAST;
>   
>   	return x2apic_mda ? dest_id : SET_APIC_DEST_FIELD(dest_id);
>   }
> 
> MSI/IOxAPIC interrupt means that source is NULL and if the target is in
> x2APIC mode, the original 'dest_id' is returned as mda => a flat logical
> xAPIC to 0x0f will get interpreted as (cluster) logical x2APIC 0xf in
> kvm_apic_match_logical_addr().
> xAPIC address are only 8 bit long so they always get delivered to x2APIC
> cluster 0, where first 16 bits work like xAPIC flat logical mode.

Ok, I was wondering whether this was the correct interpretation.  Thanks!

Paolo
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