Description
The PCI ATS Extended Capability allows peripheral devices to participate in the
caching of translations when operating under an IOMMU. Further, the ATS Page
Request Interface (PRI) Extension allows devices to handle missing mappings.
Currently, PRI is mainly used in the context of Shared Virtual Addressing,
requiring support for the Process Address Space Identifier (PASID) capability,
but other use cases such as enabling user-space driver driven device
verification and reducing memory pinning exists. In this talk we describe how
IOMMUFD may be extended in a non-SVA and non-nested context to enable user space
processes to handle page requests from VFIO PCI attached devices.
We describe our proposed changes to IOMMUFD and present a user space reference
implementation within the libvfn library. In combination with QEMU ATS/PRI
emulation, this functionality enables use-case experimentation,
hardware/software co-design and device verification for these features. We
examine in detail how ATS/PRI is tested, offering insights into the potential of
using user space testing frameworks in device validation methodologies.