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Date: Mon, 13 Aug 2012 20:32:46 +0200
From: Andreas Hartmann <andihartmann@01019freenet.de>
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Subject: Re: [Qemu-devel] [PATCH 0/3] VFIO-based PCI device assignment for
	QEMU 1.2
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To: Alex Williamson <alex.williamson@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, kvm@vger.kernel.org, aik@ozlabs.ru, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Blue Swirl <blauwirbel@gmail.com>, Avi Kivity <avi@redhat.com>

Alex Williamson wrote:
> On Mon, 2012-08-13 at 18:36 +0200, Andreas Hartmann wrote:
[...]
>> If I'm using your qemu instead of qemu from kvm-0.15 (opensuse package),
>> this error comes up when passing through a PCIe device, which works
>> absolutely fine with kvm 0.15. I would have expected, that your qemu
>> works with the legacy way of handling pcie passthrough, too (with
>> pci-stub module).
> 
> VFIO cannot work with pci-stub, the backends are fundamentally
> different.  KVM making use pci-stub to hold onto a device is actually
> one of the design problems that VFIO is meant to correct.  The other
> significant interface change is use of IOMMU groups, which is actually
> why VFIO works for some of your uses while pci-assign does not.
> 
>> This would mean, that all users get errors if they use the traditional
>> way. IOW: there are changes needed (which?) to move from kvm 0.15 to
>> your qemu version.
> 
> But the way we solve this is to make libvirt understand how to do both.
> Then it can probe the qemu/kvm binary and host system to figure out
> which is supported and use the correct device options based on what it
> finds.  Trying to do both via the same qemu command line doesn't make
> sense to me, especially when the device setup is so different.

Ok! I thought your qemu version still would understand the old way via
pci-stub. But this obviously was a misunderstanding of mine :-(.


Thanks,
Andreas