This is a patch originally introduced in LKML, which enable overrides for missing ACS capabilities. These capabilities are only available on some hight-end peocessors which might not be accessible to everyone.
Although some distributions do include this patch with their kernels, it is highly recommended to avoid using this in prodution due to potentially critical security drawbacks including VM escape.
- Build a kernel using this patchset using the attached build.bash script.
- Add pcie_acs_override=downstream OR pcie_acs_override=downstream,multifunction boot parameters.
- You also need intel_iommu=on OR amd_iommu=on boot parameters depending on your CPU.
- Run read-iommu-groups.bash to validate IOMMU device group placement.