feat: patterns/ directory + skill-impact tracker (WikiSkill-inspired)

- New patterns/ directory with 7 initial failure-mode patterns (PAT-001..007) - skill-impact.md audit trail for skill modifications - _template.md for future pattern creation - index.md updated with Patterns section - log.md entry for this change - Inspired by arXiv:2608.27454 (WikiSkill)
2026-08-30 11:16:19 +00:00
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+---
+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."