Re: [PATCH v1 3/8] iommu: Extend iommu_at[de]tach_device() for multi-device groups

[Joerg Roedel]

On Mon, Feb 14, 2022 at 11:46:26AM -0400, Jason Gunthorpe wrote:
> On Mon, Feb 14, 2022 at 03:18:31PM +0000, Robin Murphy wrote:
> 
> > Arguably, iommu_attach_device() could be renamed something like
> > iommu_attach_group_for_dev(), since that's effectively the semantic that all
> > the existing API users want anyway (even VFIO at the high level - the group
> > is the means for the user to assign their GPU/NIC/whatever device to their
> > process, not the end in itself). That's just a lot more churn.
> 
> Right

Okay, good point. I can live with an iommu_attach_group_for_dev()
interface, it is still better than making iommu_attach_device() silently
operate on whole groups.

> VFIO needs them because its uAPI is tied, but even so we keep talking
> about ways to narrow the amount of group API it consumes.
> 
> We should not set the recommended/good kAPI based on VFIOs uAPI
> design.

Agree here too. The current way groups are implemented can be turned
into a VFIO specific interface to keep its semantics and kABI. But the
IOMMU core code still needs the concept of alias groups.

Regards,

	Joerg