[Xen-devel] DomD: passthroughing an arbitrary device

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

Hi, all!

We have a use-case where we want to passthrough and arbitrary device to 
driver domain,
e.g. GPIO controller or the like (doesn't do any DMA).
I know that for device to be pass throughed it must be tied to an IOMMU, 
but in my case
the controller doesn’t have any. The problem is that it not only has 
MMIO range,
but also has its own interrupt controller, so I have to passthrough IRQs 
as well.
Here comes the limitation I face: as the controller doesn’t have any 
IOMMU I can’t
passthrough its IRQ.

Possible solutions I see could be:

1. Make it possible that Xen allows passing through devices without 
IOMMU assigned:
the problem here is that one can hack Xen then by saying that her device 
is not MMU
protected and writing/reading arbitrary memory then.

2. Make driver domain be marked somehow as a privileged one, so Xen can 
trust it and
allow passing devices without IOMMU.
Q: What if we need to pass this device to DomU?

3. Workaround by introducing a dummy IOMMU for such devices, but it 
still doesn’t
solve the problem with memory protection.

I'm hoping to hear any possible solutions/suggestions which will not 
break security and allow
passing devices at the same time.

Thank you for your time,
Oleksandr


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