s390/lowcore: reserve 96 bytes for IRB in lowcore

s390/lowcore: reserve 96 bytes for IRB in lowcore

commit 993072ee67aa179c48c85eb19869804e68887d86 upstream.

The IRB might be 96 bytes if the extended-I/O-measurement facility is
used. This feature is currently not used by Linux, but struct irb
already has the emw defined. So let's make the irb in lowcore match the
size of the internal data structure to be future proof.
We also have to add a pad, to correctly align the paste.

The bigger irb field also circumvents a bug in some QEMU versions that
always write the emw field on test subchannel and therefore destroy the
paste definitions of this CPU. Running under these QEMU version broke
some timing functions in the VDSO and all users of these functions,
e.g. some JREs.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
[bwh: Backported to 3.2: offsets of the affected fields in the 64-bit version
 of struct _lowcore are 128 bytes smaller]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>