On Fri, Aug 20, 2021 at 03:40:08PM +0000, Michael Kelley wrote:

I see that the swiotlb code gets and uses the min_align_mask field.  But
the NVME driver is the only driver that ever sets it, so the value is zero
in all other cases.  Does swiotlb just use PAGE_SIZE in that that case?  I
couldn't tell from a quick glance at the swiotlb code.

The encoding isn't all that common.  I only know it for the RDMA memory
registration format, and RDMA in general does not interact very well
with swiotlb (although the in-kernel drivers should work fine, it is
userspace RDMA that is the problem).  It seems recently a new driver
using the format (mpi3mr) also showed up.  All these should probably set
the min_align_mask.