s390/smp: enforce lowcore protection on CPU restart

As result of commit 915fea0 ("s390/smp: enable DAT before
CPU restart callback is called") the low-address protection bit
gets mistakenly unset in control register 0 save area of the
absolute zero memory. That area is used when manual PSW restart
happened to hit an offline CPU. In this case the low-address
protection for that CPU will be dropped.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Fixes: 915fea0 ("s390/smp: enable DAT before CPU restart callback is called")
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: Alexander Gordeev

arch/s390/kernel/setup.c

@@ -508,8 +508,8 @@ static void __init setup_lowcore_dat_on(void)
 	S390_lowcore.svc_new_psw.mask |= PSW_MASK_DAT;
 	S390_lowcore.program_new_psw.mask |= PSW_MASK_DAT;
 	S390_lowcore.io_new_psw.mask |= PSW_MASK_DAT;
-	__ctl_store(S390_lowcore.cregs_save_area, 0, 15);
 	__ctl_set_bit(0, 28);
+	__ctl_store(S390_lowcore.cregs_save_area, 0, 15);
 	put_abs_lowcore(restart_flags, RESTART_FLAG_CTLREGS);
 	put_abs_lowcore(program_new_psw, lc->program_new_psw);
 	for (cr = 0; cr < ARRAY_SIZE(lc->cregs_save_area); cr++)