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Re: RFC: PCI devices passthrough on Arm design proposal

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?).


Julien Grall



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