Unreal 5.5 GPu Crash Shader Compiler Bug MMU Fault error

General Feedback & Requests
1

Hello,

in Unreal 5.5 I have a rather special GPU removed error which is probably due to the shader compiler.

“Fault Description”: “A shader instruction caused an MMU fault when accessing memory.\nThis can be caused by shader bugs and binding setup issues, or possibly by a shader compiler bug or shader microcode corruption.”,
“Fault Name”: “MMU Fault Error”,

I have never seen this error message before and cannot explain it. In 5.4 every map, every sequence, every object runs without problems. In 5.5 the only workaround is to disable SM6.

Disabling Nanite for certain objects that cast a lot of shadows helps a little, but the error still occurs when scrolling around in all levels. Surprisingly, I can render every sequence perfectly. This doesn’t happen in MRQ, but it does in the free editor. I have tried all the options I know but am at a loss. I need 5.5 because of the optimized metahumans. I have updated the drivers of my 4090 and tried Studio like Game, tick here tick there in the Project Settings, but nothing works.

It’s the first time I can’t get a new Unreal version to run properly. Does anyone have a similar problem?

2

Same Problem, the GPU Crashed when enable Ray Traced Shadows. So I have to stop updating project to 5.5.

3

Same Problem,I suspect this is related to RVT

4

Disabling RT for nanite solved the problem in my case.
r.RayTracing.Nanite.Mode 0

5

I’m on 5.5.3 and I had this constant crash in my world partition map. What stopped the constant crash from happening, interestingly enough the opposite of the previous solution :

r.RayTracing.Nanite.Mode=1
r.RayTracing.Shadows.AvoidSelfIntersectionTraceDistance=10

Not sure about the number on avoid self intersection to be honest.

Crash description: in a packaged game or in-editor when walking in a specific area, my game would crash . I use World Partition, maybe I have a mesh that has intersecting geometry and the raytracing wasn’t behaving well without enabling raytracing on nanite meshes?

The only workaround would be to play the game in a tiny window.

Seemingly pertinent Crash log (honestly new to GPU profiling):

LogD3D12RHI: Error: GPU crash detected:
	- Device 0 Removed: DXGI_ERROR_DEVICE_HUNG
  {
    "Active Warps": [
      {
        "GPU PC Address": "ray_tracing_02 @ 0x00000f10",
        "Shader mapping": null,
        "Warp count": 1
      }
    ]
  },
  {
    "Faulted Warps": [
      {
        "Fault Description": "A shader instruction caused an MMU fault when accessing memory.\nThis can be caused by shader bugs and binding setup issues, or possibly by a shader compiler bug or shader microcode corruption.",
        "Fault Name": "MMU Fault Error",
        "Shader GPU PC Address": "ray_tracing_02 @ 0x00000ec0",
        "Shader mapping": null
      }
    ]
  },

If I read the GPU section LogRHI: Error: Active GPU breadcrumbs: of my log file right, the frame info (“Pipeline Graphics”) seemed to be pointing to Raytracing, Nanite, Postprocess compositeDebugPrimitives. In the “AsyncCompute” section it seemed to point to Post process or Lumen scene update.

This feels more like a band-aid and I would like to know more and what was the root cause. Hoping for more replies in this thread!