The s390 IOMMU driver currently sets the IOMMU domain's aperture to
match the device specific DMA address range of the device that is first
attached. This is not ideal. For one if the domain has no device
attached in the meantime the aperture could be shrunk allowing
translations outside the aperture to exist in the translation tables.
Also this is a bit of a misuse of the aperture which really should
describe what addresses can be translated and not some device specific
limitations.

Instead of misusing the aperture like this we can instead create
reserved ranges for the ranges inaccessible to the attached devices
allowing devices with overlapping ranges to still share an IOMMU domain.
This also significantly simplifies s390_iommu_attach_device() allowing
us to move the aperture check to the beginning of the function and
removing the need to hold the device list's lock to check the aperture.

As we then use the same aperture for all domains and it only depends on
the table properties we can already check zdev->start_dma/end_dma at
probe time and turn the check on attach into a WARN_ON().
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Link: https://lore.kernel.org/r/20221025115657.1666860-4-schnelle@linux.ibm.comSigned-off-by: Joerg Roedel <jroedel@suse.de>