Re: Virtio-IOMMU interrupt remapping design

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 6/16/25 09:20, Jason Gunthorpe wrote:
> On Sun, Jun 15, 2025 at 02:47:15PM -0400, Demi Marie Obenour wrote:
> 
>> Is a paravirtualized IOMMU with interrupt remapping something that makes
>> sense?
> 
> IMHO linking interrupt remapping to the iommu is a poor design,
> interrupt routing belongs in the irq subsystem, not in the iommu.

I agree.

> The fact AMD and Intel both coupled their interrupt routing to their
> iommu hardware is just a weird design decision. ARM didn't do this,
> for instance.

Arm did the right thing here, IMO.

> So I would not try to do this at all, you should have a
> para-virtualized IRQ interface, not an extension to virtio-iommu
> adding interrupt handling. :\

I don't disagree at all.

> AFAIK hyperv shows how to build something like this.
Would this need KVM patches?  I'm concerned that implementing this
in userspace would interact badly with the irqfd fast path.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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