On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote: > It turns out cxl actually uses it. So for now skip this patch, > although random code in drivers messing with dma ops will need to > be sorted out sooner or later.
CXL devices are "special", they bypass the classic iommu in favor of allowing the device to operate using the main processor page tables using an MMU context (so basically the device can use userspace addresses directly), akin to ATS. I think the code currently uses the nommu ops as a way to do a simple kernel mapping for kernel drivers using CXL (not userspace stuff) though. Ben.
