s390: remove critical section cleanup from entry.S

The current code is rather complex and caused a lot of subtle
and hard to debug bugs in the past. Simplify the code by calling
the system_call handler with interrupts disabled, save
machine state, and re-enable them later.

This requires significant changes to the machine check handling code
as well. When the machine check interrupt arrived while being in kernel
mode the new code will signal pending machine checks with a SIGP external
call. When userspace was interrupted, the handler will switch to the
kernel stack and directly execute s390_handle_mcck().

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 4 insertions, 10 deletions

diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index 8f8456816d83..0d7fbdfe995a 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -24,19 +24,19 @@ void enabled_wait(void)
 {
 	struct s390_idle_data *idle = this_cpu_ptr(&s390_idle);
 	unsigned long long idle_time;
-	unsigned long psw_mask;
+	unsigned long psw_mask, flags;
 
-	trace_hardirqs_on();
 
 	/* Wait for external, I/O or machine check interrupt. */
 	psw_mask = PSW_KERNEL_BITS | PSW_MASK_WAIT | PSW_MASK_DAT |
 		PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK;
 	clear_cpu_flag(CIF_NOHZ_DELAY);
 
+	local_irq_save(flags);
 	/* Call the assembler magic in entry.S */
 	psw_idle(idle, psw_mask);
+	local_irq_restore(flags);
 
-	trace_hardirqs_off();
 
 	/* Account time spent with enabled wait psw loaded as idle time. */
 	write_seqcount_begin(&idle->seqcount);
@@ -118,22 +118,16 @@ u64 arch_cpu_idle_time(int cpu)
 
 void arch_cpu_idle_enter(void)
 {
-	local_mcck_disable();
 }
 
 void arch_cpu_idle(void)
 {
-	if (!test_cpu_flag(CIF_MCCK_PENDING))
-		/* Halt the cpu and keep track of cpu time accounting. */
-		enabled_wait();
+	enabled_wait();
 	local_irq_enable();
 }
 
 void arch_cpu_idle_exit(void)
 {
-	local_mcck_enable();
-	if (test_cpu_flag(CIF_MCCK_PENDING))
-		s390_handle_mcck();
 }
 
 void arch_cpu_idle_dead(void)