[PATCH] arm64/irq: use NMI to send stop IPI

[Pingfan Liu]

Like other arches, both 'kexec -l' and 'kexec -p' expect to use NMI to
interrupt other cpus in order to capture cpus tightly to a known state.

So for both of the cases, try to use NMI IPI if irqchip supports NMI.

Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Julien Thierry <julien.thierry at arm.com>
To: linux-arm-kernel at lists.infradead.org
---
 arch/arm64/kernel/smp.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 18e9727..ff61e2c 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -884,6 +884,31 @@ static void ipi_cpu_crash_stop(unsigned int cpu, struct pt_regs *regs)
 }
 
 /*
+ * Overlapped with the counterpart in do_handle_IPI(), only just for nmi purpose
+ */
+static irqreturn_t nmi_ipi_handler(int irq, void *data)
+{
+	unsigned int cpu = smp_processor_id();
+	int ipinr = irq - ipi_irq_base;
+
+	switch (ipinr) {
+	case IPI_CPU_STOP:
+		local_cpu_stop();
+		unreachable();
+		break;
+
+	case IPI_CPU_CRASH_STOP:
+		if (IS_ENABLED(CONFIG_KEXEC_CORE)) {
+			ipi_cpu_crash_stop(cpu, get_irq_regs());
+
+			unreachable();
+		}
+		break;
+	}
+	return IRQ_NONE;
+}
+
+/*
  * Main handler for inter-processor interrupts
  */
 static void do_handle_IPI(int ipinr)
@@ -902,10 +927,12 @@ static void do_handle_IPI(int ipinr)
 		generic_smp_call_function_interrupt();
 		break;
 
+	/* If NMI IPI is not supported */
 	case IPI_CPU_STOP:
 		local_cpu_stop();
 		break;
 
+	/* If NMI IPI is not supported */
 	case IPI_CPU_CRASH_STOP:
 		if (IS_ENABLED(CONFIG_KEXEC_CORE)) {
 			ipi_cpu_crash_stop(cpu, get_irq_regs());
@@ -989,6 +1016,14 @@ void __init set_smp_ipi_range(int ipi_base, int n)
 	for (i = 0; i < nr_ipi; i++) {
 		int err;
 
+		if (i == IPI_CPU_CRASH_STOP || i == IPI_CPU_STOP) {
+			err = request_percpu_nmi(ipi_base + i, nmi_ipi_handler,
+				"NMI-IPI", &cpu_number);
+			if (!err)
+				continue;
+
+			pr_warn("Fail to request nmi for NMI-IPI\n");
+		}
 		err = request_percpu_irq(ipi_base + i, ipi_handler,
 					 "IPI", &cpu_number);
 		WARN_ON(err);
@@ -1038,6 +1073,7 @@ void smp_send_stop(void)
 
 		if (system_state <= SYSTEM_RUNNING)
 			pr_crit("SMP: stopping secondary CPUs\n");
+		/* NMI is expected, but it is subject to the irq line's ability */
 		smp_cross_call(&mask, IPI_CPU_STOP);
 	}
 
@@ -1084,6 +1120,7 @@ void crash_smp_send_stop(void)
 	atomic_set(&waiting_for_crash_ipi, num_other_online_cpus());
 
 	pr_crit("SMP: stopping secondary CPUs\n");
+	/* NMI is expected, but it is subject to the irq line's ability */
 	smp_cross_call(&mask, IPI_CPU_CRASH_STOP);
 
 	/* Wait up to one second for other CPUs to stop */
-- 
2.7.5