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 23:18:42 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Kr?má? <rkrcmar@...hat.com>
CC:	"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>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH v8 03/13] KVM: Define a new interface
 kvm_intr_is_single_vcpu()



> -----Original Message-----
> From: Paolo Bonzini [mailto:pbonzini@...hat.com]
> Sent: Friday, September 18, 2015 12:00 AM
> To: Radim Krčmář
> Cc: Wu, Feng; alex.williamson@...hat.com; joro@...tes.org;
> mtosatti@...hat.com; eric.auger@...aro.org; kvm@...r.kernel.org;
> iommu@...ts.linux-foundation.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, I don't think Radim clarify your concern, right? Since mda is 8-bit, it
is wrong with mda >> 16, this is your concern, right?

Thanks,
Feng

> 
> Paolo