Linux 5.13 Yanks A NVIDIA NVLink Driver For Lack Of Open-Source User

The VFIO changes for the Linux 5.13 kernel aren't particularly exciting this cycle but one of the changes does raise some eyebrows with the VFIO NVIDIA NVLink2 driver being removed. This driver is being removed as it shouldn't have been even added in the first place for lack of an open-source client/user exercising it.

The vfio_pci_nvlink2 driver is being stripped out of the Linux 5.13 kernel. This VFIO NVLink2 driver is used for supporting this NVIDIA interconnect standard on POWER9 systems using Volta-based NVIDIA V100 GPUs.

While there is since NVLink 3.0 and 4.0, the NVLink 2.0 for POWER9 with Volta GPUs is seeing the VFIO support removed not for being obsolete but because there isn't an open-source user.

This VFIO NVLink2 driver was added back in 2018 to the Linux kernel. The VFIO pull for Linux 5.13 simply notes that this vfio-pci NVLink2 code is being removed. But the actual removal patch by longtime upstream kernel developer Christoph Hellwig explains, "This driver never had any open userspace (which for VFIO would include VM kernel drivers) that use it, and thus should never have been added by our normal userspace ABI rules."

So after two years in mainline, the driver is now being removed as while it's an open-source driver, for now at least it only jives when working with proprietary software bits. Surprising though that this wasn't caught in the first place once being upstreamed given how rigorous the kernel developers tend to be over ensuring open-source users or at least test code for exercising exposed kernel interfaces.