Re: RFC: PCI devices passthrough on Arm design proposal

[Julien Grall <julien@xxxxxxx>]

On 17/07/2020 20:17, Oleksandr wrote:
> I would like to clarify regarding an IOMMU driver changes which should 
> be done to support PCI pass-through properly.
> Design document mentions about SMMU, but Xen also supports IPMMU-VMSA 
> (under tech preview now). It would be really nice if the required 
> support is extended to that kind of IOMMU as well.
> May I clarify what should be implemented in the Xen driver in order to 
> support PCI pass-through feature on Arm? 
I would expect callbacks to:
    - add a PCI device
    - remove a PCI device
    - assign a PCI device
    - deassign a PCI device

AFAICT, they are already existing. So it is a matter of plumbing. This 
would then be up to the driver to configure the IOMMU correctly.
> Should the IOMMU H/W be 
> "PCI-aware" for that purpose?
The only requirement is that your PCI devices are behind an IOMMU :). 
Other than that the IOMMU can mostly be configured the same way as you 
would do for the non-PCI devices. The main difference would be how you 
find the master ID.
I am aware that on some platforms, the masterID may be shared between 
multiple PCI devices. In that case, we would need to have a way to 
assign all the devices to the same guest (maybe using group?).
Cheers,

--
Julien Grall