Re: [PATCH RFC 21/26] dma-buf: Add the Physical Address List DMA mapping type

[Jason Gunthorpe <jgg@nvidia.com>]

On Sat, May 09, 2026 at 01:31:56PM +0800, Xu Yilun wrote:
> > Would you be open to an in-between? The exporter and importer both
> > have information that should not leak into each other's drivers. 
> > 
> > What if the dmabuf mapping type core code was the only thing that had
> > access to *BOTH*? The exporter provides the address data, the importer
> > provides the iommu_domain. The core code, and only the core code, has
> > both and does the required operation?
> 
> I think that may not work for KVM. On IOMMU side, IOMMUFD acts as the
> address space (iova) manager and dma_api/IOMMU driver acts as the
> actual page table mapper. But for KVM, it is both. KVM doesn't allow
> another component to provide an unknown address space (GPA space) and
> say "map it", so doesn't expose to other components about "KVM domain".
> 
> Even if we expose "KVM domain", KVM still acts as the importer and the
> mapper, is it wierd to say we trust KVM-the-mapper, but don't trust
> KVM-the-as-manager?
> 
> Is it also wierd that we trust IOMMU-the-mapper, but don't trust
> IOMMUFD-the-as-manager? There are more IOMMU drivers than IOMMUFD...

Yeah, it doesn't work well for kvm, and yes it is really weird and
worse that phys in every way..

Jason