Description of problem:
I'm getting the error 'host doesn't support VFIO PCI interface'  on a VM with no VFIO devices; it *has* got a host USB device which it's upset at, so I guess there's two problems, 1) Why it's upset at the USB and 2) it's giving the wrong error.
I'll attach the full XML, but the relavant bit is:
    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x04e8'/>
        <product id='0x3321'/>
      </source>
      <address type='usb' bus='0' port='1'/>
    </hostdev>

(my printer)
I can see in the qemu log:
2017-03-27T14:58:03.166472Z qemu-system-x86_64: libusb_release_interface: -4 [NO_DEVICE]
libusb: error [_open_sysfs_attr] open /sys/bus/usb/devices/1-1.2/bConfigurationValue failed ret=-1 errno=2

which doesn't make much sense given the device is:
Bus 003 Device 003: ID 04e8:3321 Samsung Electronics Co., Ltd 


Version-Release number of selected component (if applicable):
libvirt-daemon-3.2.0-1.fc26.x86_64

How reproducible:
100%??

Steps to Reproduce:
1. virsh start print   on VM defined with attached XML
2.
3.

Actual results:


Expected results:


Additional info:
This was working on f25, but as I remember didn't on earlier versions (but it gave a sane USB error)

LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin QEMU_AUDIO_DRV=spice /usr/bin/qemu-kvm -name guest=print,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-print/master-key.aes -machine pc-i440fx-2.4,accel=kvm,usb=off,vmport=off -cpu SandyBridge -m 1024 -realtime mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid c373cf7f-e23a-41f3-b678-a25b1cd169bd -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-1-print/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=discard -no-hpet -no-shutdown -global PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -device nec-usb-xhci,id=usb,bus=pci.0,addr=0x6 -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 -drive file=/home/vmimages/print.qcow2,format=qcow2,if=none,id=drive-virtio-disk0 -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x7,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=27 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:02:20:e6,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -chardev spicevmc,id=charchannel0,name=vdagent -device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel0,id=channel0,name=com.redhat.spice.0 -chardev socket,id=charchannel1,path=/var/lib/libvirt/qemu/channel/target/domain-1-print/org.qemu.guest_agent.0,server,nowait -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel1,id=channel1,name=org.qemu.guest_agent.0 -device usb-tablet,id=input0,bus=usb.0,port=2 -spice port=5900,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on -device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2 -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev spicevmc,id=charredir0,name=usbredir -device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=3 -device usb-host,hostbus=1,hostaddr=4,id=hostdev0,bus=usb.0,port=1 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8 -msg timestamp=on
char device redirected to /dev/pts/27 (label charserial0)
main_channel_link: add main channel client
red_qxl_set_cursor_peer:
inputs_connect: inputs channel client create
main_channel_handle_parsed: agent start
2017-03-27T14:58:03.132052Z qemu-system-x86_64: terminating on signal 15 from pid 1112
dummy_channel_client_disconnect: rcc=0x55d8e2971190 (channel=0x55d8e2fce120 type=5 id=0)
snd_channel_unref: SndChannel=0x55d8e2afc000 freed
dummy_channel_client_disconnect: rcc=0x55d8e33c3190 (channel=0x55d8e2fce220 type=6 id=0)
snd_channel_unref: SndChannel=0x55d8e3370000 freed
red_channel_client_default_disconnect: rcc=0x55d8e33be180 (channel=0x55d8e2fcf100 type=9 id=0)
2017-03-27T14:58:03.166472Z qemu-system-x86_64: libusb_release_interface: -4 [NO_DEVICE]
libusb: error [_open_sysfs_attr] open /sys/bus/usb/devices/1-1.2/bConfigurationValue failed ret=-1 errno=2