Subject: [PATCH v2 1/3] powerpc: use NMI IPI for smp_send_stop

From: Nicholas Piggin <[email-masked]>
Date: Sun, 1 Apr 2018 20:36:13 +1000

Use the NMI IPI rather than smp_call_function for smp_send_stop.
Have stopped CPUs hard disable interrupts rather than just soft
disable.

This function is used in crash/panic/shutdown paths to bring other
CPUs down as quickly and reliably as possible, and minimizing their
potential to cause trouble.

Avoiding the Linux smp_call_function infrastructure and (if supported)
using true NMI IPIs makes this more robust.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/smp.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index cfc08b099c49..db88660bf6bd 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -565,7 +565,11 @@ void crash_send_ipi(void (*crash_ipi_callback)(struct pt_regs *))
 }
 #endif
 
+#ifdef CONFIG_NMI_IPI
+static void stop_this_cpu(struct pt_regs *regs)
+#else
 static void stop_this_cpu(void *dummy)
+#endif
 {
 	/* Remove this CPU */
 	set_cpu_online(smp_processor_id(), false);
@@ -577,7 +581,11 @@ static void stop_this_cpu(void *dummy)
 
 void smp_send_stop(void)
 {
+#ifdef CONFIG_NMI_IPI
+	smp_send_nmi_ipi(NMI_IPI_ALL_OTHERS, stop_this_cpu, 1000000);
+#else
 	smp_call_function(stop_this_cpu, NULL, 0);
+#endif
 }
 
 struct thread_info *current_set[NR_CPUS];
-- 
2.16.3