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Re: [Xen-devel] GPU passthrough on ARM

On 01/25/2018 04:17 AM, Julien Grall wrote:

On 24/01/18 22:10, Martin Kelly wrote:


Does anyone know if GPU passthrough is supported on ARM? (e.g. for a GPU integrated into an ARM SoC). I checked documentation and the code, but I couldn't tell for sure.

If so, what are the hardware requirements for it? If not, is it feasible to do in the future?

Xen Arm supports device integrated into an ARM SoC. In general we highly recommend to have the GPU behind an IOMMU. So passthrough would be fully secure.

Does your platform has an IOMMU? If so which one? Do you know if the GPU is behind it?

It would be possible to do passthrough without IOMMU, but that's more complex and would require some hack in Xen to make sure the guest memory is direct mapped (e.g guest physical address = host physical address).

For more documentation on how to do it (see [1] and [2]).


[1] https://events.static.linuxfound.org/sites/events/files/slides/talk_5.pdf
[2] https://wiki.xen.org/images/1/17/Device_passthrough_xen.pdf

Hi Julien,

Thanks very much for the information. I'm looking at the Renesas R-Car H3 R8A7795, which has an IOMMU (using the Linux ipmmu-vmsa driver in drivers/iommu/ipmmu-vmsa.c). Looking at the device tree for it (r8a7795.dtsi), it appears you could pass through the display@feb00000 node for the DRM driver.

I did notice this patch series, which didn't get merged:


Presumably that driver would be needed in Xen.

Are there any gotchas I'm missing? Is GPU passthrough on ARM something that is "theoretically doable" or something that has been done already and shown to be performant?

Thanks again,

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