s390-bios: Skip writing iplb location to low core for ccw ipl

The architecture states that the iplb location is only written to low
core for list directed ipl and not for traditional ccw ipl. If we don't
skip this then operating systems that load by reading into low core
memory may fail to start.

We should also not write the iplb pointer for network boot as it might
overwrite content that we got via network.

Fixes: 9bfc04f9 ("pc-bios: s390x: Save iplb location in lowcore")
Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201030122823.347140-1-borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

pc-bios/s390-ccw/main.c

@@ -43,7 +43,9 @@ void write_subsystem_identification(void)
 
 void write_iplb_location(void)
 {
-    lowcore->ptr_iplb = ptr2u32(&iplb);
+    if (cutype == CU_TYPE_VIRTIO && virtio_get_device_type() != VIRTIO_ID_NET) {
+        lowcore->ptr_iplb = ptr2u32(&iplb);
+    }
 }
 
 unsigned int get_loadparm_index(void)