KVM: s390: Prevent memslots outside the ASCE range

KVM: s390: Prevent memslots outside the ASCE range

With KVM_S390_VM_MEM_LIMIT_SIZE, userspace can set the highest address
allowed for the VM. Creating a memslot that lies over the maximum
address does not make sense and is only a potential source of bugs.

Prevent creation of memslots over the maximum address, and prevent the
maximum address from being reduced below the end of existing memslots.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260602142356.169458-9-imbrenda@linux.ibm.com>