Fixing Proxmox eGPU PCIe Passthrough Boot Issues

- APU: Ryzen 5600GT (iGPU passed through)

- eGPU: AMD Radeon 6700XT

- Connection: M.2 to Oculink adapter

- Proxmox with VFIO configured

The system boots normally with the external GPU disconnected. With it connected, Proxmox hangs shortly after VFIO assignment.

GRUB and UEFI run normally. The freeze happens during kernel initialization, right after IOMMU grouping and VFIO binding.

- iGPU: IOMMU group 03:00

- eGPU: IOMMU group 07:00

- amdgpu driver blacklisted

- Improper VFIO binding order for multiple GPUs

- ACS/IOMMU grouping conflicts via M.2 adapter

- PCIe bifurcation or lane instability

- BIOS Above 4G decoding disabled

- Kernel trying to initialize amdgpu before blacklist applies

- Bind both GPUs explicitly to vfio-pci using their device IDs in /etc/modprobe.d.

- Confirm that the kernel parameters include: amd_iommu=on iommu=pt

- Enable "Above 4G Decoding" in the BIOS.

- Disable CSM and make sure the system boots in pure UEFI mode.

- Try booting with: initcall_blacklist=sysfb_init

- Remove the amdgpu blacklist temporarily to test whether a driver conflict is the cause.

- Some M.2 adapters lack proper PCIe hotplug handling.

- IOMMU groups may change when external devices are present.

- Lane sharing between the NVMe drive and the GPU can cause instability.

- Boot into recovery mode with the GPU attached and check dmesg.

Why does Proxmox boot without the eGPU but not with it?

Kernel initialization changes when it detects additional PCIe devices, especially when VFIO and blacklisted drivers are involved.

Can two GPUs be passed through simultaneously?

Yes, as long as each one is properly isolated and bound to vfio-pci.

Is M.2 to Oculink stable for passthrough?

It can work, but that depends heavily on the motherboard's PCIe topology and the BIOS configuration.

Should amdgpu be blacklisted?

Only if the device is fully bound to vfio-pci. Otherwise, test without the blacklist to see how the system behaves.