Linux kernel (drivers/iommu/intel): On VT-d scalable mode with VMD enabled, RID2PASID setup fails for devices behind

Impact

On VT-d scalable mode with VMD enabled, RID2PASID setup fails for devices behind the VMD bridge, the device fails to join its IOMMU group, and the failure path adds the device info to a list it is already on. The result is a kernel BUG and a panic during boot or PCI enumeration. Practically this means a node configured for both NVMe VMD and the scalable-mode IOMMU that passthrough needs does not stay up - and scalable mode is exactly what you enable to do PASID-based device assignment.

Who can reach it

Not tenant-reachable. Triggered by host configuration: Intel VT-d in scalable mode plus VMD enabled in BIOS, on Sapphire Rapids class platforms. The panic happens during device enumeration, so it hits at boot or on PCI rescan, and needs host/firmware-level access to set up. Worth tracking because it is the combination a GPU node with NVMe VMD and PASID passthrough naturally lands on.

What to do

Fixed in 5.13 / 5.14 per this record; run a kernel at or beyond those on Intel nodes, or apply the linked stable commits. Interim: do not enable VMD and IOMMU scalable mode together on the same host - disable VMD in BIOS on nodes that need scalable-mode passthrough.

References