On Fri, Jun 17, 2022 at 01:54:05AM -0700, Christoph Hellwig wrote:

There is a bunch of code an comments in the iommu type1 code that suggest we can pin memory that is not page backed.

AFAIK you can.. The whole follow_pte() mechanism allows raw PFNs to be loaded into the type1 maps and the pin API will happily return them. This happens in almost every qemu scenario because PCI MMIO BAR memory ends up routed down this path.

Thanks, Jason