Re: [Qemu-devel] [PATCH v5 00/18] IOMMU: Enable interrupt remapping for Intel IOMMU

[Radim Krčmář]

2016-04-28 17:18+0800, Peter Xu:
> On Thu, Apr 28, 2016 at 09:19:28AM +0200, Jan Kiszka wrote:
>> Instead of fiddling with irq routes for the IOAPIC - where we don't need
>> it -, I would suggest to do the following: Send IOAPIC events via
>> kvm_irqchip_send_msi to the kernel. Only irqfd users (vhost, vfio)
>> should use the pattern you are now applying to the IOAPIC: establish
>> static routes as an irqfd is set up, and that route should be translated
>> by the iommu first, register an IEC notifier to update any affected
>> route when the iommu translation changes.
> 
> Yes, maybe that's the right thing to do. Or say, when split irqchip,
> IOAPIC can avoid using GSI routes any more. If with that, I should
> also remove lots of things, like: IEC notifiers for IOAPIC, and all
> things related to msi route sync-up in IOAPIC codes with KVM (so I
> suppose we will save 24 gsi route entries for KVM, which sounds
> good).

Sadly, we can't get rid of those GSI routes.  KVM uses them to decide
whether it should forward EOI to userspace.  And QEMU also has to remap
them, because KVM uses dest_id for that decision.