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

[Marc Zyngier]

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.

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.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...