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Gotcha: GRUB hangs without ACPI/APIC features in the libvirt domain

Symptom

Rocky 9 VM boots to GRUB, shows: 

Welcome to GRUB!
Probing EDD (edd=off to disable)... ok
_
Then hangs indefinitely. Kernel never loads. No network traffic, no DHCP lease. VGA screenshot confirms the same screen after 5+ minutes.

Root cause

The dmacvicar/libvirt OpenTofu provider v0.9.7 does NOT set ACPI or APIC features by default. The virt-install --os-variant rocky9 command DOES set them (via the osinfo database). Without ACPI:

  • GRUB can initialize basic hardware (EDD probe passes)
  • But the kernel loader path relies on ACPI tables for device enumeration, power management, and interrupt routing
  • The kernel either can't load or loads into a broken state

Interestingly, the VM consumes 100% CPU while hung — GRUB is apparently spinning on something that requires ACPI but doesn't time out.

Fix

In the OpenTofu libvirt_domain resource: 

features = {
  acpi = true
  apic = {}    # apic is an object, not a bool — empty {} enables it
}

cpu = {
  mode = "host-passthrough"
}

Debugging approach that found this

  1. Took VGA screenshots (virsh screenshot) — confirmed genuine hang
  2. Tested the RAW image with virt-install --os-variant rocky9 → booted fine
  3. Compared virsh dumpxml of the working domain vs the broken one
  4. The diff was: features (acpi, apic) and CPU mode
  5. Added features to the ToFu config → VM booted

How to prevent

Any OpenTofu config using dmacvicar/libvirt v0.9.x for modern Linux guests MUST include features { acpi = true; apic = {} }. This is the provider's most critical gotcha because the default (no features) produces a domain that looks correct but silently fails to boot.

Environment

  • dmacvicar/libvirt provider v0.9.7
  • OpenTofu v1.11.6
  • Rocky Linux 9.7 GenericCloud image
  • QEMU 8.2.2 on Ubuntu 24.04