On Mon, Jun 16, 2025 at 12:53:40PM -0400, Demi Marie Obenour wrote: > > 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.
I don't know. I think you get the same issues even if you did virtio-iommu irq handling, it shouldn't be any different. I'm not sure there even is a fast path here, remapping happens during initial vector setup/affinity change only. That isn't fast path. So long as the MSI is delivered to the correct CPU vector entirely in KVM it seems OK. And the hyperv approach of asking the hypervisor for the addr/data pair to achieve certain parameters will work alot better with existing Linux than trying to build a iommu emulation where the guest is building its own private addr/data pairs :\ Jason
