On Tue, Jul 29, 2025 at 02:54:13PM -0600, Logan Gunthorpe wrote:

On 2025-07-28 17:11, Jason Gunthorpe wrote:

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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