Cable modem not working after pci passthrough configured

philled

Renowned Member
May 25, 2015
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1
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I got a few VMs installed and running today. The first one was a Sophos UTM which is like pfSense. It has three NICs two of which are on a PCI card. This was all working great until I set up the last VM which is a home theatre PVR with a DVB-T card. To use the DVB-T card I had to set up PCI passthrough. As soon as I did this I started having problems with the network card and it wouldn't connect to the cable modem any more.

I think this may be one of those IOMMU problems where all PCI devices in the same IOMMU group can only be assigned to a single VM.

Any ideas how I can resolve this?

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I've got some more info on this.

After enabling IOMMU in grub, running update-grub and rebooting doesn't cause a problem:
GRUB_CMDLINE_LINUX_DEFAULT="quiet intel_iommu=on"

At this point the Sophos VM can still connect to all three NICs and start up a connection with the cable modem on of them. (BTW I should have mentinoed the 3 NICs are present as one on-board NIC with the other two being part of a dual-NIC PCI card).

Now, if I enable IOMMU in the vmnumber.conf file of one of the other VMs in order to pass through a DVB-T PCI card and then start that VM, the problem starts.
hostpci0: 05:02.2,driver=vfio
As soon as the second VM with the pci passthrough gets past its boot prompt the Sophos VM on the cable modem loses its connection. It happens instantaneously so I'm convinced the two events are related. I've seen on other forums posts about IOMMU groups but I don't know how that works on Proxmox and it's not an area I understand at all.

Can anyone offer some advice please?
 

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