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, 16 insertions, 7 deletions

diff --git a/arch/s390/kernel/nmi.c b/arch/s390/kernel/nmi.c
index 0a487fae763e..86c8d5370e7f 100644
--- a/arch/s390/kernel/nmi.c
+++ b/arch/s390/kernel/nmi.c
@@ -148,7 +148,6 @@ void s390_handle_mcck(void)
 	local_mcck_disable();
 	mcck = *this_cpu_ptr(&cpu_mcck);
 	memset(this_cpu_ptr(&cpu_mcck), 0, sizeof(mcck));
-	clear_cpu_flag(CIF_MCCK_PENDING);
 	local_mcck_enable();
 	local_irq_restore(flags);
 
@@ -333,7 +332,7 @@ NOKPROBE_SYMBOL(s390_backup_mcck_info);
 /*
  * machine check handler.
  */
-void notrace s390_do_machine_check(struct pt_regs *regs)
+int notrace s390_do_machine_check(struct pt_regs *regs)
 {
 	static int ipd_count;
 	static DEFINE_SPINLOCK(ipd_lock);
@@ -342,6 +341,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 	unsigned long long tmp;
 	union mci mci;
 	unsigned long mcck_dam_code;
+	int mcck_pending = 0;
 
 	nmi_enter();
 	inc_irq_stat(NMI_NMI);
@@ -400,7 +400,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 		 */
 		mcck->kill_task = 1;
 		mcck->mcck_code = mci.val;
-		set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 
 	/*
@@ -420,8 +420,7 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 			mcck->stp_queue |= stp_sync_check();
 		if (S390_lowcore.external_damage_code & (1U << ED_STP_ISLAND))
 			mcck->stp_queue |= stp_island_check();
-		if (mcck->stp_queue)
-			set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 
 	/*
@@ -442,12 +441,12 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 	if (mci.cp) {
 		/* Channel report word pending */
 		mcck->channel_report = 1;
-		set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 	if (mci.w) {
 		/* Warning pending */
 		mcck->warning = 1;
-		set_cpu_flag(CIF_MCCK_PENDING);
+		mcck_pending = 1;
 	}
 
 	/*
@@ -462,7 +461,17 @@ void notrace s390_do_machine_check(struct pt_regs *regs)
 		*((long *)(regs->gprs[15] + __SF_SIE_REASON)) = -EINTR;
 	}
 	clear_cpu_flag(CIF_MCCK_GUEST);
+
+	if (user_mode(regs) && mcck_pending) {
+		nmi_exit();
+		return 1;
+	}
+
+	if (mcck_pending)
+		schedule_mcck_handler();
+
 	nmi_exit();
+	return 0;
 }
 NOKPROBE_SYMBOL(s390_do_machine_check);