Description of problem:
boot a windows guest passthrough the USB3.0 stick to it redirected from usb-host with xHCI controller, but fail to detect it in guest, and check the speed of the usb via HMP monitor is 1.5 Mb/s.

Version-Release number of selected component (if applicable):
host info:
kernel-3.9.0-0.rc4.45.el7.x86_64
qemu-kvm-1.4.0-1.el7.x86_64
seabios-1.7.2-0.2.gita810e4e7.el7.x86_64
guest info:
windows: win2012/win8 64bit

How reproducible:
100%

Steps to Reproduce:
1.get the usb3.0 info from host.
# lsusb | grep CompUSA
Bus 010 Device 005: ID 1516:6221 CompUSA
# lsusb -v
...
Bus 010 Device 005: ID 1516:6221 CompUSA 
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               3.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0         9
  idVendor           0x1516 CompUSA
  idProduct          0x6221
...
Binary Object Store Descriptor:
  bLength                 5
  bDescriptorType        15
  wTotalLength           22
  bNumDeviceCaps          2
  USB 2.0 Extension Device Capability:
    bLength                 7
    bDescriptorType        16
    bDevCapabilityType      2
    bmAttributes   0x00000002
      Link Power Management (LPM) Supported
  SuperSpeed USB Device Capability:
    bLength                10
    bDescriptorType        16
    bDevCapabilityType      3
    bmAttributes         0x00
    wSpeedsSupported   0x000e
      Device can operate at Full Speed (12Mbps)
      Device can operate at High Speed (480Mbps)
      Device can operate at SuperSpeed (5Gbps)
    bFunctionalitySupport   1
      Lowest fully-functional device speed is Full Speed (12Mbps)
    bU1DevExitLat          10 micro seconds
    bU2DevExitLat        2047 micro seconds
Device Status:     0x0000
  (Bus Powered)
...
2.boot a windows guest redirected with passthrough the USB3.0 stick from remote via usb-host with xHCI controller.
e.g:# /usr/libexec/qemu-kvm -S -M pc-i440fx-1.4 -cpu SandyBridge -enable-kvm -m 4096 -smp 2,sockets=2,cores=1,threads=1 -no-kvm-pit-reinjection -name sluo-test -uuid ed09fa10-6ffe-4811-a42f-0294afcb5a42 -rtc base=localtime,clock=host,driftfix=slew -device virtio-serial-pci,id=virtio-serial0,max_ports=16,vectors=0,bus=pci.0,addr=0x3 -chardev socket,id=channel1,path=/tmp/helloworld1,server,nowait -device virtserialport,chardev=channel1,name=com.redhat.rhevm.vdsm,bus=virtio-serial0.0,id=port1 -chardev socket,id=channel2,path=/tmp/helloworld2,server,nowait -device virtserialport,chardev=channel2,name=com.redhat.rhevm.vdsm,bus=virtio-serial0.0,id=port2 -drive file=/home/sluo/windows_server_2012_x64_bak.qcow2,if=none,id=drive-system-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop,serial=QEMU-DISK1 -device virtio-scsi-pci,bus=pci.0,addr=0x4,id=scsi0 -device scsi-hd,bus=scsi0.0,drive=drive-system-disk,id=system-disk,bootindex=1 -netdev tap,id=hostnet0,vhost=off,script=/etc/qemu-ifup -device virtio-net-pci,netdev=hostnet0,id=virtio-net-pci0,mac=08:2e:5f:0a:0d:b1,bus=pci.0,addr=0x5,bootindex=2 -device virtio-balloon-pci,id=ballooning,bus=pci.0,addr=0x6 -global PIIX4_PM.disable_s3=0 -global PIIX4_PM.disable_s4=0 -serial unix:/tmp/ttyS0,server,nowait -qmp tcp:0:4444,server,nowait -k en-us -boot menu=on -vnc :1 -spice disable-ticketing,port=5931 -monitor stdio -device nec-usb-xhci,id=xhci0 -chardev spicevmc,name=usbredir,id=usbredirchardev1 -device usb-redir,chardev=usbredirchardev1,id=usbredirdev1,debug=3
3.connect the VM via 'remote-viewer spice://xxx:xxx'.
4.put the USB3.0 stick in the usb-host and press 'cont' in monitor.
5.check the usb info via HMP monitor.
(qemu) info usb
(qemu) info qtree
6.check the usb disk in guest.

Actual results:
after step 5, the speed of the usb is 1.5Mb/s.
(qemu) info usb
  Device 0.0, Port 1, Speed 1.5 Mb/s, Product USB Redirection Device
(qemu) info qtree
...
  dev: i440FX-pcihost, id ""
    irq 0
    bus: pci.0
      type PCI
      dev: nec-usb-xhci, id "xhci0"
        msi = on
        msix = on
        intrs = 16
        slots = 64
        p2 = 4
        p3 = 4
        addr = 07.0
        romfile = <null>
        rombar = 1
        multifunction = off
        command_serr_enable = on
        class USB controller, addr 00:07.0, pci id 1033:0194 (sub 1af4:1100)
        bar 0: mem at 0xfebf0000 [0xfebf3fff]
        bus: xhci0.0
          type usb-bus
          dev: usb-redir, id "usbredirdev1"
            chardev = usbredirchardev1
            debug = 3
            filter = <null>
            bootindex = -1
            port = <null>
            full-path = on
            addr 0.0, port 1, speed 1.5, name USB Redirection Device
...
after step 6, it fail to detect the usb disk in guest via device manager.

Expected results:
the speed of the usb should be 5000 Mb/s, and can be detected in guest and used correctly.

Additional info: