On Thu, Feb 27, 2025 at 11:32:42AM -0400, Jason Gunthorpe wrote:

On Thu, Feb 27, 2025 at 11:21:28AM +0000, Robin Murphy wrote:

quoted

All I'm saying is to hide the callback detail in the IOMMUFD code because
being IOMMUFD modular is unique to IOMMUFD and not the rest of the core
code's problem.

Maybe we could use a global function pointer set/cleared on iommufd
module load?

Regardless, we need to first find a way for the core code to tell if
the domain is iommufd owned or not.

We should also make it so we can tell if dma-iommu.c is linked to that
domain (eg vfio or the default_domain), then we can do the iova_cookie
move without changing the destruction flows. This would be the missing
union struct tag you mentioned in the other email.

What I've been thinking of is changing type into flags. I think we
have now removed type from all drivers so this should be a small
enough work.

Nicolin should be able to look into some followup here, it is not a
small change.

quoted

And frankly otherwise, what even is the benefit of moving the iova_cookie
pointer into the union if we have to replace it with another whole pointer
to make it work?

It makes a lot more semantic sense that the domain owners all share a
single "private data" pointer.

I found a bit confusing to use "owner" as the domain->owner isn't
the same thing in this context. Maybe it should be "driver_ops"?

Then, "owner" could be another op structure that holds the owner-
specific things, such as:
	enum iommu_domain_owner { DMA/VFIO/IOMMUFD}; // or flag?
	union {
		iova_cookie;  // DMA
		msi_cookie;   // VFIO
		iommufd_hwpt; // IOMMUFD
	}
	(*sw_msi);
?

Thanks
Nicolin