---
pattern_id: PAT-004
title: "VFIO GPU passthrough fails — missing softdep + incomplete DRM blacklist"
category: infrastructure
severity: high
status: active
first_observed: 2026-07
last_updated: 2026-08-30
related_systems: [proxmox-cluster, rke2-kubernetes]
related_solution_docs:
  - docs/solutions/bug-fixes/2026-07-24-vfio-pci-module-loading-race-condition.md
  - docs/solutions/bug-fixes/2026-07-21-amd-gpu-passthrough-rombar.md
related_skills: []
---

# VFIO GPU passthrough fails — missing softdep + incomplete DRM blacklist

## Symptom

GPU passthrough to a VM fails intermittently or consistently. Symptoms include:
- `/dev/dri/renderD128` missing in the guest
- `amdgpu` driver not loading in guest
- Kernel BUG in host dmesg
- GPU device visible in `lspci` but not bound to `vfio-pci`

## Root Cause

Two intertwined issues:

1. **Module loading race condition**: Without `softdep amdgpu pre: vfio-pci`, the amdgpu
   driver races to bind the GPU before vfio-pci can claim it. Normal bind time ~2.4s;
   racing bind time ~302s (or never succeeds).

2. **Incomplete DRM blacklist**: If `drm` and `drm_kms_helper` are not blacklisted, the
   kernel's DRM subsystem grabs the GPU before vfio-pci, preventing passthrough.

## Mitigation

Apply to the PVE host's modprobe config:
```bash
# /etc/modprobe.d/blacklist-drm.conf
blacklist drm
blacklist drm_kms_helper

# /etc/modprobe.d/amdgpu-vfio.conf
softdep amdgpu pre: vfio-pci
```
Then rebuild initramfs and reboot:
```bash
update-initramfs -u -k all
reboot
```

Also ensure `rombar=1` in the VM config for AMD GPUs (PCI ID 1002:xxxx):
```
# /etc/pve/qemu-server/<VMID>.conf
hostpci0: 0000:XX:YY.Z,pcie=1,rombar=1,x-vga=1
```

## Prevention

- Always configure `softdep` + DRM blacklist BEFORE attempting GPU passthrough on a new node
- Add to provisioning scripts (Ansible/Tofu) for any node with AMD GPU intended for passthrough
- ROCm 7.x: gfx1150 supported, gfx1036 NOT supported — verify GPU compute ISA before assignment

## Evidence

- Observed on ms-a2-1 (race condition, Jul 2026) and worker-05/VM 102 (kernel BUG, rombar)
- Solution docs: `2026-07-24-vfio-pci-module-loading-race-condition.md`,
  `2026-07-21-amd-gpu-passthrough-rombar.md`
- MEMORY.md entry: "GPU:2 active—Immich(CT111/n5pro gfx1150)+Frigate(CT120/px7). ROCm7.14=gfx1150 supported,gfx1036 NOT."