KVM: s390: pv: add export before import

KVM: s390: pv: add export before import

Due to upcoming changes, it will be possible to temporarily have
multiple protected VMs in the same address space, although only one
will be actually active.

In that scenario, it is necessary to perform an export of every page
that is to be imported, since the hardware does not allow a page
belonging to a protected guest to be imported into a different
protected guest.

This also applies to pages that are shared, and thus accessible by the
host.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20220628135619.32410-7-imbrenda@linux.ibm.com
Message-Id: <20220628135619.32410-7-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>