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[Qemu-devel] Question about qtest and IOMMU

From: Peter Xu
Subject: [Qemu-devel] Question about qtest and IOMMU
Date: Wed, 29 Jun 2016 14:32:21 +0800
User-agent: Mutt/1.5.24 (2015-08-30)

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.


-- peterx

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