Re: [RFC PATCH 01/12] dma-buf: Introduce dma_buf_get_pfn_unlocked() kAPI

[Christoph Hellwig]

On Wed, Jan 15, 2025 at 09:55:29AM +0100, Simona Vetter wrote:
> I think for 90% of exporters pfn would fit, but there's some really funny
> ones where you cannot get a cpu pfn by design. So we need to keep the
> pfn-less interfaces around. But ideally for the pfn-capable exporters we'd
> have helpers/common code that just implements all the other interfaces.

There is no way to have dma address without a PFN in Linux right now.
How would you generate them?  That implies you have an IOMMU that can
generate IOVAs for something that doesn't have a physical address at
all.

Or do you mean some that don't have pages associated with them, and
thus have pfn_valid fail on them?  They still have a PFN, just not
one that is valid to use in most of the Linux MM.