Proxmox GPU Passthrough Failure Traced to HBA Conflict, Not the GPU

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A Proxmox 8 host configured for PCIe passthrough of an NVIDIA RTX A4000 into an Ubuntu 24.04 VM repeatedly failed to start the guest, with QEMU exiting silently and leaving no console output. Host-side dmesg logs revealed IRQ allocation failures and VFIO interrupt remapping errors at VM startup, pointing to a deeper hardware conflict rather than a misconfigured GPU setup. Despite following standard passthrough steps — including VT-d, IOMMU, OVMF BIOS, and q35 machine type — the issue persisted across multiple troubleshooting sessions. The root cause turned out to be a Host Bus Adapter (HBA) in the system, not the GPU itself, making the fault difficult to identify because error messages implicated the wrong device. The passthrough was being set up to accelerate Filecoin sealing workloads, specifically the TreeRC tree-building phase, which can drop from two to three hours down to fifteen to twenty minutes with GPU acceleration.

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