Re: KVM devices assignment; PCIe AER?

Chris Wright
2010-10-26T20:42:28Z

* Etienne Martineau (etmartin101@gmail.com) wrote:
> ***Background context:
> We are using kvm on a x86 based platform. For performance reason, we
> use devices assignment. The type of devices we have to deal with is
> mostly custom ASICs but we also have standard stuff (ex 82599EB
> 10-GigabitSR-IOV).
>
> AER handling in guest VM is very important to us. Most of our
> drivers assume timely notification in cases of PCIe AER. Failure to
> provide such support will result in very undesireable behavior at
> the other end :)
>
> In our cases, AER is not strictly function of the hardware 'quality'
> but also tied to the way the user can interact with the system (by
> pulling a card on the fly for example).
>
> ***Q35, VFIO:
> I'm aware of the PCIe Q35 chipset work that Isaku is working on. I
> have a college that is working actively on merging the change into
> our qemu-kvm branch.
>
> I'm also familiar with VFIO. I've seen the work from Alex on the
> qemu VFIO front. Not too sure how this is going to work on qemu-kvm?
> OR maybe it's because I'm confused about the long term plan for user
> space [qemu vs qemu-kvm] branch?

The Plan (TM) is for qemu-kvm to be just a staging branch for qemu.
There are a few bits left in qemu-kvm (I'm sure you're aware since
you're working with them ;) that aren't yet upstream. The device
assignment code is one of those bits.

Ideally, we could get KVM out of the business of being a device driver
for assigned host devices and move all of that functionality to VFIO.
And when looking at adding significant new functionality like AER,
scoping VFIO would be very useful.

> ***One of the aspect I'm not clear is the strategy for
> device-assignment under KVM?
> A) Move to VFIO; [/dev/iommu, /dev/vfio]

Long term, hopefully VFIO

> B) KVM as a driver for the assigned devices; [sysfs/ ioctls..]

Short term (i.e. current qemu-kvm tree...this is what we have now and
will continue to until plan A) gets more mature).

thanks,
-chris