Environment:
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Host OS (ia32/ia32e/IA64):ia32e
Guest OS (ia32/ia32e/IA64):ia32e
Guest OS Type (Linux/Windows):linux
kvm.git Commit:54ad89b05ec49b90790de814647b244d3d2cc5ca
qemu.git Commit:c47c61be8dcd91689c8fc77776db924d684c3b39
Host Kernel Version:3.17.0-rc1
Hardware:HSW-Desktop

Bug detailed description:
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the 4-ports 82576 can detect 2 ports when add "intel_iommu=on pci=assign-busses" in kernel of grub.
the 4-ports 82576 can detect 4 ports without "intel_iommu=on pci=assign-busses"
when add "intel_iommu=on", 4-ports 82576 detected 4 ports.
when add "pci=assign-busses" ,the 4-ports 82576 can detect 2 ports.

note: 
kernel version: 3.0.0+ (kvm+qemu-kvm:e72ef590_fda19064)
1.the 4-ports 82576 can detect 4 ports when add "intel_iommu=on pci=assign-busses".
2. when add "intel_iommu=on" or "pci=assign-busses" to boot the system, 4-ports 82576 detected 4 ports


Reproduce steps:
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1. add "intel_iommu=on pci=assign-busses" in kernel of grub
2. boot up the system
3. lspci | grep Eth

Current result:
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4-ports 82576 detect 2 ports

Expected result:
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4-ports 82576 detect 4 ports



Basic root-causing log:
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