Unreal Engine EXCEPTION_ILLEGAL_INSTRUCTION on Proxmox VM with Intel Xeon Silver 4214R

Development Getting Started & Setup
1

Hello everyone,

I’m running a Windows 11 virtual machine on Proxmox in order to use Unreal Engine. My physical server has an Intel Xeon Silver 4214R CPU, and I’ve set up GPU pass-through with an NVIDIA A4000 (drivers are up to date and verified via benchmarks).

My issue is that whenever I try different CPU configurations in Proxmox for the VM, Unreal Engine either won’t start at all, or it crashes with an EXCEPTION_ILLEGAL_INSTRUCTION error. Specifically:

  • x86-64-v2-AES: Unreal Engine launches, but immediately logs the EXCEPTION_ILLEGAL_INSTRUCTION error.
  • All other CPU models (including host, cascadelake-server, etc.): Unreal Engine doesn’t start at all.

I’ve confirmed with CPU-Z inside the VM that the virtual CPU passes through the following flags from the physical CPU: SSE4.2, AVX, and AVX2. The GPU appears to be recognized correctly by Windows and is working fine under benchmarks, so I’m fairly confident the issue is CPU-related.

Has anyone experienced a similar problem or found a workaround to ensure Unreal Engine runs correctly in a Proxmox virtualized Windows 11 environment with AVX/AVX2 instructions enabled? Any tips or guidance would be greatly appreciated.

Thank you!

2

Hi @Arspen
Let’s see…
To correct the EXCEPTION_ILLEGAL_INSTRUCTION exception in your Proxmox VM for Unreal Engine with GPU passthrough, follow these instructions:

CPU Model Configuration:

Deploy cpu: host,hidden=1 to your Proxmox VM configuration in order to passthrough more features from your host CPU.
Try different CPU models (e.g., qemu64, kvm64, or sandybridge) in order to avoid compatibility problems with Unreal Engine.
Check CPU Features:

Ensure AVX and AVX2 are being passed properly, and also verify Unreal Engine isn’t trying to utilize unsupported instructions (e.g., AVX-512).
Windows 11 Compatibility:

Make sure your VM is configured to support Windows 11 features like TPM and Secure Boot.
Unreal Engine Settings:

Update Unreal Engine to the newest build.
Tune settings within Unreal Engine, such as setting the renderer or disabling optimizations.
Proxmox Version & Virtualization Extensions

Ensure your Proxmox version is updated, with CPU virtualization extensions enabled (vmx for Intel).