Re: [RFT][PATCH v1 6/6] vfio: Replace phys_pfn with phys_page for vfio_pin_pages()

Christoph Hellwig
2022-06-20T05:52:06Z

On Mon, Jun 20, 2022 at 12:00:46AM -0300, Jason Gunthorpe wrote:
> 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.

Indeed, my read wasn't deep enough. Which means that we can't change
the ->pin_pages interface to return a struct pages array, as we don't
have one for those.