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I'm working on a Ubuntu KVM server. It's Ubuntu 14.04 LTS with kernel 3.19. The motherboard is the Gigabyte ga-990fxa-ud5 r5 with bios ver. 3. I have qeum/kvm 2.2 installed. I have IOMMU on in the kernel and can pass my video cards and usb through. I have a Intel 82576 four port card and it is detected and shows SR-IOV capability. I have installed the latest verion of the IGB driver for it. Seems to be fine as it is attached to the ports on the card.

My issue is that when I put "max_vfs=4" in a file under modprobe.d and reboot, no virtual functions show up. I also have one "modprobe -r igb" and then "modprobe igb max_vfs=4" as suggested by people. Nothing. I just can't seem to program this server and make the virtual functions show up.

Is it even possible with this motherboard? Is the kernel the issue?

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Firstly, rebooting is not required when creating VFs. Infact rebooting will remove the VFs(if any created).

Use the below command to view the number of VFs for a specific PCI device:

cat /sys/bus/pci/devices/<pci-address>/max_vfs

It should be zero when no VF is created, now create a VF using the below command:

echo 1 > /sys/bus/pci/devices/<pci-address>/max_vfs
view the VF using "lspci" command
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  • Vikrant, thanks for you post. I did try that and I get the following error: "echo: write error: cannot allocate memory" Is this due to a motherboard limitation, or could it be something else? I looked in the iommu folder and found that the interfaces are in a group with a PCI bridge. Is that the issue? Like, it's trying to issue commands to all three of them for the vfs and it fails for the bridge and the network interfaces remain unchanged due to that? Also, what is the deal with the igbvf driver? Does that load into the kernel automatically when you add an interface, or do you have to add it
    – user544342
    May 15, 2016 at 18:25
  • @ThomasStruss On some motherboards, you may have to add this boot parameter to make linux override BIOS PCI configuration: pci=assign-busses Then retry the echo 1 cmd shown in answer. May 25, 2016 at 12:19

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