Re: [PATCH 05/10] PCI/P2PDMA: Export pci_p2pdma_map_type() function

[Leon Romanovsky <leon@kernel.org>]

On Tue, Jul 29, 2025 at 02:54:13PM -0600, Logan Gunthorpe wrote:
> 
> 
> On 2025-07-28 17:11, Jason Gunthorpe wrote:
> >> If the dma mapping for P2P memory doesn't need to create an iommu
> >> mapping then that's fine. But it should be the dma-iommu layer to decide
> >> that.
> > 
> > So above, we can't use dma-iommu.c, it might not be compiled into the
> > kernel but the dma_map_phys() path is still valid.
> 
> This is an easily solved problem. I did a very rough sketch below to say
> it's really not that hard. (Note it has some rough edges that could be
> cleaned up and I based it off Leon's git repo which appears to not be
> the same as what was posted, but the core concept is sound).

I started to prepare v2, this is why posted version is slightly
different from dmabuf-vfio branch.

In addition to what Jason wrote. there is an extra complexity with using
state. The wrappers which operate on dma_iova_state assume that all memory,
which is going to be mapped, is the same type: or p2p or not.

This is not the cased for HMM/RDMA users, there you create state in
advance and get mixed type of pages.

Thanks