Re: [PATCH] vfio: Enable VFIO device for powerpc

[Paolo Bonzini]

On 26/08/2015 20:54, Paul Mackerras wrote:
> On Wed, Aug 26, 2015 at 11:34:26AM +0200, Alexander Graf wrote:
>> On 13.08.15 03:15, David Gibson wrote:
>>> ec53500f "kvm: Add VFIO device" added a special KVM pseudo-device which is
>>> used to handle any necessary interactions between KVM and VFIO.
>>>
>>> Currently that device is built on x86 and ARM, but not powerpc, although
>>> powerpc does support both KVM and VFIO.  This makes things awkward in
>>> userspace
>>>
>>> Currently qemu prints an alarming error message if you attempt to use VFIO
>>> and it can't initialize the KVM VFIO device.  We don't want to remove the
>>> warning, because lack of the KVM VFIO device could mean coherency problems
>>> on x86.  On powerpc, however, the error is harmless but looks disturbing,
>>> and a test based on host architecture in qemu would be ugly, and break if
>>> we do need the KVM VFIO device for something important in future.
>>>
>>> There's nothing preventing the KVM VFIO device from being built for
>>> powerpc, so this patch turns it on.  It won't actually do anything, since
>>> we don't define any of the arch_*() hooks, but it will make qemu happy and
>>> we can extend it in future if we need to.
>>>
>>> Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
>>> Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>

This patch (commit 178a787502123) did not select CONFIG_KVM_VFIO, so the
patch did nothing---except causing build failures which I fixed in
commit 0af574be32cdd ("KVM: PPC: do not compile in vfio.o
unconditionally", 2016-03-21) by making the patch a total no-op.

Is KVM_VFIO really needed, and if so can this patch be fixed?

Thanks,

Paolo