s390/nmi: consistently enable machine checks in trap_init()

The kernel starts with machine checks disabled (machine check mask bit in
the PSW is zero), and machine checks are enabled when trap_init() is
called. The rationale is that this allows to assume that the system is
initialized up to a certain point before the machine check handler may be
invoked.

However the implementation is incomplete: all new PSW masks in lowcore have
the machine check mask bit. This means that e.g. for any early program
check machine checks are enabled within the program check handler. This
contradicts the whole point of enabling machine checks at a single place.

Change this and initialize all new PSWs in lowcore so they have the machine
check mask bit not set. Set the bit in all masks in trap_init(). This way
machine check enabling is consistent.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
index 1d2aa448d103..8cb3832a1621 100644
--- a/arch/s390/kernel/traps.c
+++ b/arch/s390/kernel/traps.c
@@ -286,6 +286,17 @@ static void __init test_monitor_call(void)
 
 void __init trap_init(void)
 {
+	unsigned long flags;
+	struct ctlreg cr0;
+
+	local_irq_save(flags);
+	cr0 = local_ctl_clear_bit(0, CR0_LOW_ADDRESS_PROTECTION_BIT);
+	psw_bits(S390_lowcore.external_new_psw).mcheck = 1;
+	psw_bits(S390_lowcore.program_new_psw).mcheck = 1;
+	psw_bits(S390_lowcore.svc_new_psw).mcheck = 1;
+	psw_bits(S390_lowcore.io_new_psw).mcheck = 1;
+	local_ctl_load(0, &cr0);
+	local_irq_restore(flags);
 	local_mcck_enable();
 	test_monitor_call();
 }