How to properly enable IOMMU on Linux?

Questions
3

I can explain this:

  • On Intel you need intel_iommu=on to turn it on
  • On AMD the kernel will automatically turn the IOMMU on
  • On AMD you can further ensure all devices are isolated and none are exempted with amd_iommu=force_isolation
    • with linux 6.13 and higher this has recently caused black screens on newer amdgpus, it will likely be fixed in the future
  • Regardless of both you should use iommu=force to enable it in cases where it may not be used such as low memory situation. This afaik will not turn it on, only ensure it stays on in more cases.
  • And you should also enable strict TLB invalidation via iommu.strict=1, this ensures mappings are always accurately set instead of lazily updated upon changes
  • Lastly you want iommu.passthrough=0 this ensures the IOMMU is always enforced even for DMA
  • efi=disable_early_pci_dma can be used to minimize ability of DMA before full IOMMU initialization, however this can commonly cause issues with GPUs getting stuck at a black screen, so test it on your system before setting it permanently
8 Likes