Re: Virtio-IOMMU interrupt remapping design

Michael S. Tsirkin
2025-06-17T19:44:35Z

On Mon, Jun 16, 2025 at 10:20:31AM -0300, 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.
>
> 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.

why does it matter in which device it resides?
Way I see it, there is little reason to remap interrupts
without also using an iommu, so why not a single device.
what did I miss?

> 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. :\
>
> AFAIK hyperv shows how to build something like this.
>
> Jason