[PATCH] s390/setup: fix boot crash for machine without EDAT-1

[Martin Schwidefsky]

The fix to make WARN work in the early boot code created a problem
on older machines without EDAT-1. The setup_lowcore_dat_on function
uses the pointer from lowcore_ptr[0] to set the DAT bit in the new
PSWs. That does not work if the kernel page table is set up with
4K pages as the prefix address maps to absolute zero.

To make this work the PSWs need to be changed with via address 0 in
form of the S390_lowcore definition.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 94f85ed3e2 ("s390/setup: fix early warning messages")
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
---
 arch/s390/kernel/setup.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 65b22ef5141a..12934e8fbb91 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -451,13 +451,12 @@ static void __init setup_lowcore_dat_off(void)
 
 static void __init setup_lowcore_dat_on(void)
 {
-	struct lowcore *lc;
-
-	lc = lowcore_ptr[0];
-	lc->external_new_psw.mask |= PSW_MASK_DAT;
-	lc->svc_new_psw.mask |= PSW_MASK_DAT;
-	lc->program_new_psw.mask |= PSW_MASK_DAT;
-	lc->io_new_psw.mask |= PSW_MASK_DAT;
+	__ctl_clear_bit(0, 28);
+	S390_lowcore.external_new_psw.mask |= PSW_MASK_DAT;
+	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_set_bit(0, 28);
 }
 
 static struct resource code_resource = {
-- 
2.16.4


-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.