12

One of my customers had a problem with a Xeon E5 machine: they were having one gpu (I believe it was an NVIDIA one) hanging and they solved by adding the

intel_iommu = igfx_off

in the grub loader.

What is this value and what does it? I read around but couldn't just figure that out in simple terms

user3498783
  • 193
  • 1
  • 1
  • 4

1 Answers1

17

Quoting from the "Intel-IOMMU.txt" file included in the Linux kernel documentation:

"If you encounter issues with graphics devices, you can try adding option intel_iommu=igfx_off to turn off the integrated graphics engine. If this fixes anything, please ensure you file a bug reporting the problem."

Apparently the GPU in this case was not working properly with the DMAR (DMA Remapping) feature provided by the Intel chipset. Using the "igfx_off" parameter allows the GPU to access the physical memory directly without going through the DMAR.

The purpose of the DMAR feature is to enable things like direct assignment of hardware to virtualized guests. If you have to use the "igfx_off" parameter then you probably won't be able to use this GPU in such a direct-assigned virtualization scenario.

Ondra Žižka
  • 43,948
  • 41
  • 217
  • 277
N7EKB
  • 197
  • 1
  • 9
  • 1
    For reference: https://www.kernel.org/doc/Documentation/Intel-IOMMU.txt – Peter May 15 '19 at 07:22
  • 1
    I don’t fully understand your answer. The quoted text from Intel-IOMMU.txt sounds like `intel_iommu=igfx_off` turns off the integrated graphics engine completely. Your answer suggests that integrated graphics will still work, just not within virtualization. Can you please clarify. Thx. – Peter May 15 '19 at 07:24
  • @Peter, yes that's what I was trying to say. Only virtualization would be affected. – N7EKB Jan 15 '20 at 21:09