s390x/pci: add support for guests that request direct mapping

s390x/pci: add support for guests that request direct mapping

When receiving a guest mpcifc(4) or mpcifc(6) instruction without the T
bit set, treat this as a request to perform direct mapping instead of
address translation.  In order to facilitate this, pin the entirety of
guest memory into the host iommu.

Pinning for the direct mapping case is handled via vfio and its memory
listener.  Additionally, ram discard settings are inherited from vfio:
coordinated discards (e.g. virtio-mem) are allowed while uncoordinated
discards (e.g. virtio-balloon) are disabled.

Subsequent guest DMA operations are all expected to be of the format
guest_phys+sdma, allowing them to be used as lookup into the host
iommu table.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-ID: <20250226210013.238349-2-mjrosato@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>