Support for the VFIO container /dev/vfio/vfio

configname: CONFIG_VFIO_CONTAINER

Linux Kernel Configuration
└─>Device Drivers
└─>VFIO Non-Privileged userspace driver framework
└─>Support for the VFIO container /dev/vfio/vfio
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
The VFIO container is the classic interface to VFIO for establishing
IOMMU mappings. If N is selected here then IOMMUFD must be used to
manage the mappings.

Unless testing IOMMUFD say Y here.