Re: [Qemu-devel] Question about qtest and IOMMU

[Jan Kiszka]

On 2016-06-29 08:32, Peter Xu wrote:
> Hi, all,
> 
> I am thinking about whether it's possible to write up a unit test
> program for emulated IOMMUs (of course, Intel IOMMU would be the first
> one). This can provide us the chance to do quick functional regression
> tests for IOMMU just like other devices, as well as customized test
> sequences which is hard to do in real guests (e.g., specific cache
> invalidations, error injections), etc..
> 
> I see that current qtest framework cannot support well on testing
> IOMMUs. For DMA remapping, things would be quite smooth. The problem
> is that, we still do not have a complete test framework on the
> interrupts. E.g., currently qtest is still an acceleration type, in
> which we have no vCPUs, as well as interrupt chips like APICs (please
> correct me if I am wrong). It's even further if we want to test
> something like kernel irqchips with QEMU. Not sure whether it's
> possible to do test based on a much realistic VM (e.g., with KVM
> enabled, but just keep the CPUs stall?).
> 
> I'd say that IOMMU is still experimental, and there are only limited
> number of patches for it (so maybe we do not need a unit test at all).
> Just want to post this idea out, to see:
> 
> - Whether we need a IOMMU unit test after all?
> 
> - Whether there is other potential consumer who has similar needs to
>   IOMMU, so that we can see whether try to move qtest a step further
>   if there are common requirements.
> 

Adding David and Valentine as we were discussing this need in the
context of the AMD IOMMU as well: You cannot test errors with workload
(like Linux) that do not trigger them in normal conditions.

Jan

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