[PATCH] KVM: arm/arm64: vgic: Don't notify EOI for non-SPIs

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier at arm.com]
> Sent: Thursday, December 01, 2016 10:58 AM
> To: Shameerali Kolothum Thodi; Paolo Bonzini; Radim Krčmář
> Cc: Catalin Marinas; kvmarm at lists.cs.columbia.edu; linux-arm-
> kernel at lists.infradead.org; kvm at vger.kernel.org
> Subject: Re: [PATCH] KVM: arm/arm64: vgic: Don't notify EOI for non-
> SPIs
> 
> On 01/12/16 10:28, Shameerali Kolothum Thodi wrote:
> > Hi Marc,
> >
> >> -----Original Message-----
> >> From: kvmarm-bounces at lists.cs.columbia.edu [mailto:kvmarm-
> >> bounces at lists.cs.columbia.edu] On Behalf Of Marc Zyngier
> >> Sent: Thursday, December 01, 2016 9:26 AM
> >> To: Paolo Bonzini; Radim Krčmář
> >> Cc: Catalin Marinas; kvmarm at lists.cs.columbia.edu; linux-arm-
> >> kernel at lists.infradead.org; kvm at vger.kernel.org
> >> Subject: [PATCH] KVM: arm/arm64: vgic: Don't notify EOI for non-SPIs
> >>
> >> When we inject a level triggerered interrupt (and unless it is
> backed
> >> by the physical distributor - timer style), we request a maintenance
> >> interrupt. Part of the processing for that interrupt is to feed to
> the
> >> rest of KVM (and to the eventfd subsystem) the information that the
> >> interrupt has been EOIed.
> >>
> >> But that notification only makes sense for SPIs, and not PPIs (such
> as
> >> the PMU interrupt). Skip over the notification if the interrupt is
> not
> >> an SPI.
> >
> > Just to clarify my understanding, the maintenance interrupt is
> generated
> > for cases where there is no mapping of virt to phys interrupts
> > (ie, ICH_LR HW bit is not set). And I was under the impression that
> > kvm_notify_acked_irq will eventually deactivate the interrupt on
> distributor
> > for such cases. Its not clear to me how the deactivation is done
> > otherwise.
> >
> > Could you please help me to understand this better.
> 
> kvm_notify_acked_irq() doesn't do *anything* at the distributor level,
> ever (it has no idea of anything GIC-specific anyway). It's sole job is
> to signal the rest of the stack that an interrupt has been EOIed in the
> guest.

Thanks Marc. Understood. I got confused by the kvm_set_irq in the 
kvm_notify_acked_irq path. 

> For these interrupts, which are purely virtual, there is absolutely
> nothing to do at the physical distributor level anyway. Furthermore,
> kvm_notify_acked_irq doesn't know about per-cpu interrupt, which is why
> we cannot notify them.

Just to confirm, that means for any phys interrupt(PPI/SPI) to be injected
to the Guest, the mapping bit has(HW bit set) to be used.

Thanks,
Shameer