Description of problem:
When assigned VFs or PFs to a PV guest, VFs can be seen as attatched in Dom0, but not in DomU.

Version-Release number of sellected component:
xen:host:kernel_version: 2.6.18-240.el5xen
host_arch:x86_64
guest:guest_name: RHEL-Sever-6.0
Xen:guest:kernel_version: kernel-2.6.32-71.el6.x86_64
host:xen_version: xen-3.0.3-122.el5

How reproducible:
100%

Steps to Reproduce:
1- Make sure you have enabled VT-d(for Intel machine) or AMD-Vi(for AMD machine) in BIOS.
2- SR-IOV supported hardware. (for example: Intel 82576 NIC) for VF assignment.
3- boot up xen host with iommu and pci_pt_e820_access enabled
   Add "iommu=1" in kernel line
   Add "pci_pt_e820_access=on" in module line
4- Check whether PF enabled in Dom0
   Example:
   # lspci | grep 82576
   Two PF NIC should be shown

0000:0f:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)

5-  Reload igb (driver for intel 82576 NIC) module with max_vfs=7 parameter
   # modprobe -r igb
   # modprobe igb max_vfs=7
6- Load pciback driver:
   # modprobe pciback
   check whether pciback was loaded:
   # lsmod | grep pciback
7- install a REHEL6 PV guest via virt-manager
8- assign one of the VF on host to the PV guest via virt-manager

Actual Results:
1- Check whether N VFs attached to guest correctly in Dom0:
   # xm pci-list ${DomU_ID}
   domain   bus   slot   func
   0    f     10     0      

2- Check whether N VFs attached to guest correctly in DomU:
   [guest]# lspci
   None of the VFs can be seen in lspci output.

Expected Results:
1- Check whether N VFs attached to guest correctly in Dom0:
   # xm pci-list ${DomU_ID}
   Corresponding number of VFs should be shown.

2- Check whether N VFs attached to guest correctly in DomU:
   [guest]# lspci


Additional info:
   Same result via xm commands.
   Similar experiments for only one VF, and PF of Intel 82576 NIC, BCM5764M and USB controller are implemented. In these case, also only in Dom0 we can see the attached PFs or VFs.
   Same test passed with RHEL5.5 PV guest and REHEL6.0 	HVM guest.