Passthrough more than 4 PCIe devices to Proxmox 4.4 and 5 guests

By default in Proxmox 4.4 and 5.0, you are unable to pass through more than 4 PCIe devices to the guest. If you try, you’ll get an error when attempting to start the VM which reads:

vm 100 - unable to parse value of 'hostpci4' - unknown setting 'hostpci4'

Passed-through PCIe devices are attached to the four ports called “ich9-pcie-port-{1,2,3,4}” which are defined in /usr/share/qemu-server/pve-q35.cfg. These ports occupy PCIe function numbers 0-3, leaving function numbers 4-7 unused.

It’s a simple matter to add definitions for an extra 4 ports to use up those spare function numbers in /usr/share/qemu-server/pve-q35.cfg:

[device "ich9-pcie-port-5"]
 driver = "ioh3420"
 multifunction = "on"
 bus = "pcie.0"
 addr = "1c.4"
 port = "5"
 chassis = "5"

[device "ich9-pcie-port-6"]
 driver = "ioh3420"
 multifunction = "on"
 bus = "pcie.0"
 addr = "1c.5"
 port = "6"
 chassis = "6"

[device "ich9-pcie-port-7"]
 driver = "ioh3420"
 multifunction = "on"
 bus = "pcie.0"
 addr = "1c.6"
 port = "7"
 chassis = "7"

[device "ich9-pcie-port-8"]
 driver = "ioh3420"
 multifunction = "on"
 bus = "pcie.0"
 addr = "1c.7"
 port = "8"
 chassis = "8"

Note that this file is a bit sensitive to extra whitespace on empty lines, so make sure empty lines are fully empty. Then we just need to patch the VM configuration parser in /usr/share/perl5/PVE/ and /usr/share/perl5/PVE/QemuServer/ to accept “hostpci4” through “hostpci7” as valid:

Patch for Proxmox 4.4

Patch for Proxmox 5

Do note that this patch doesn’t add support for PCI devices in those new positions, only PCIe ones.

After applying those patches, stopping my VMs, and restarting the pve-manager service (service restart pve-manager on Proxmox 4.4 and systemctl restart pve-manager.service on Proxmox 5, not sure if this is really required or not), VM configurations like this that pass through 5 PCIe devices now become valid:

hostpci0: 03:00,pcie=1,x-vga=on
hostpci1: 00:1a.0,pcie=1
hostpci2: 00:1d.0,pcie=1
hostpci3: 82:00.0,pcie=1
hostpci4: 81:00.0,pcie=1

This allowed me to pass through 3 USB controllers, an NVMe SSD and a graphics card to my macOS VM!

This modification is made at your own risk! There might have been a good reason why the number of PCIe devices was limited to 4 (although I suspect that the reason was that the number of available PCI device numbers was running out).

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