From: Jason Gunthorpe <jgg@nvidia.com>
Sent: Tuesday, September 21, 2021 11:42 PM

 - Delete the iommufd_ctx->lock. Use RCU to protect load, erase/alloc does
   not need locking (order it properly too, it is in the wrong order), and
   don't check for duplicate devices or dev_cookie duplication, that
   is user error and is harmless to the kernel.

I'm confused here. yes it's user error, but we check so many user errors
and then return -EINVAL, -EBUSY, etc. Why is this one special?