Enable PCI Passthrough in Proxmox VE

Requirements

Hardware needs to support IOMMU (Input/Output Memory Management Unit) - Normally all newer systems support this kind of feature

Configure Proxmox

To enable the passthrough support mainly two components needs to be adapted

The bootloader(GRUB) config
The kernel modules

GRUB config

Depending on your system you need to add the following parameters to your GRUB_CMDLINE_LINUX_DEFAULT property

Parameter	Function
intel_iommu=on	Activates IOMMU for Intel systems
amd_iommu=on	Activates IOMMU for AMD systems
iommu=pt	pt stands for passthrough and increases the performance

For Intel based systems

GRUB_CMDLINE_LINUX_DEFAULT="quiet intel_iommu=on iommu=pt"

For AMD based systems

GRUB_CMDLINE_LINUX_DEFAULT="quiet amd_iommu=on iommu=pt"

Kernel modules

Module	Function	Source
vfio	Virtual Function I/O	¹
vfio_iommu_type1		²
vfio_pci	For devices that are not managed by libvirt	³
vfio_virqfd	Not needed with PVE 8+ (Kernel 6.2) - It's no longer a seperate module	⁴

# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
vfio
vfio_iommu_type1
vfio_pci
#vfio_virqfd

Apply configs

After restarting your system the configured settings should be applied automatically, and you're ready to go and pass-through your PCI devices.

To check if everything works as expected you can ask your system for details

dmesg | grep -e DMAR -e IOMMU

...
[    0.052157] DMAR: IOMMU enabled
...
[    0.389246] DMAR: Intel(R) Virtualization Technology for Directed I/O

lsmod | grep vfio

vfio_pci               16384  1
vfio_pci_core          86016  1 vfio_pci
vfio_iommu_type1       49152  1
vfio                   65536  8 vfio_pci_core,vfio_iommu_type1,vfio_pci
iommufd                94208  1 vfio
irqbypass              12288  3 vfio_pci_core,kvm

Sources

https://www.thomas-krenn.com/de/wiki/Proxmox_PCIe_Passthrough_aktivieren
https://enterprise-support.nvidia.com/s/article/understanding-the-iommu-linux-grub-file-configuration