Re: [RFC PATCH kernel] vfio: Skip checking for IOMMU_CAP_CACHE_COHERENCY on POWER and more

On Fri, Jul 01, 2022 at 11:40:26PM +0000, Tian, Kevin wrote:

> But a bigger problem to me is how dma ownership is managed now on
> POWER. Previously it was guarded by BUG_ON and vfio_group_viable().

Yes. Simply removing or deferring this can't be good.

I think the solution is to not do iommu operations if there are no
iommu_ops, including allocating a blocking domain or trying to change
the domain - but continue to do all the refcounting/etc.

It is just another crufty work around for platforms that don't support
the iommu framework..

Jason