How to express "externally managed" IOMMU domains for VFIO/IOMMUFD ?

[Teddy Astie <teddy.astie@xxxxxxxxxx>]

Hello,

On Xen, for PV-IOMMU [1], we have IOMMU support in Dom0, which in 
particular allows using VFIO and IOMMUFD from Dom0.

However, its interactions with PCI Passthrough are unclear, and it would 
be preferable to let the kernel handle some of this logic. That would 
for instance avoid situations where toolstack causes Xen and Linux to go 
out of sync on where devices belong.

On Xen, we have a dedicated hypercalls for moving a device into another 
guest (so it no longer belongs in Dom0, at far as DMA is concerned).

But it looks like there are no way to describe that idea of "attach that 
device to this VM" nor "the device is in a VM"; which makes that 
impracticable.

There may be things that could be done with the vIOMMU objects, but 
there would be no "parent domain" in such case, as said earlier it 
doesn't exist in the IOMMU subsystem.

What is expected to be done instead ?

Teddy

[1] https://www.youtube.com/watch?v=pLMGRgEJ-Eg


--
Teddy Astie | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech