linux-kernel - [PATCH v3 1/4] arm64: smp: Introduce a new IPI as IPI_CALL_NMI

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Date:   Thu,  3 Sep 2020 17:35:09 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     maz@...nel.org, catalin.marinas@....com, will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, tglx@...utronix.de,
        jason@...edaemon.net, julien.thierry.kdev@...il.com,
        dianders@...omium.org, daniel.thompson@...aro.org,
        jason.wessel@...driver.com, kgdb-bugreport@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Sumit Garg <sumit.garg@...aro.org>
Subject: [PATCH v3 1/4] arm64: smp: Introduce a new IPI as IPI_CALL_NMI_FUNC

Introduce a new inter processor interrupt as IPI_CALL_NMI_FUNC that
can be invoked to run special handlers in NMI context. One such handler
example is kgdb_nmicallback() which is invoked in order to round up CPUs
to enter kgdb context.

As currently pseudo NMIs are supported on specific arm64 platforms which
incorporates GICv3 or later version of interrupt controller. In case a
particular platform doesn't support pseudo NMIs, IPI_CALL_NMI_FUNC will
act as a normal IPI which can still be used to invoke special handlers.

Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
---
 arch/arm64/include/asm/smp.h |  1 +
 arch/arm64/kernel/smp.c      | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
index 2e7f529..e85f5d5 100644
--- a/arch/arm64/include/asm/smp.h
+++ b/arch/arm64/include/asm/smp.h
@@ -89,6 +89,7 @@ extern void secondary_entry(void);
 
 extern void arch_send_call_function_single_ipi(int cpu);
 extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
+extern void arch_send_call_nmi_func_ipi_mask(const struct cpumask *mask);
 
 #ifdef CONFIG_ARM64_ACPI_PARKING_PROTOCOL
 extern void arch_send_wakeup_ipi_mask(const struct cpumask *mask);
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index b6bde26..1b4c07c 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -74,6 +74,7 @@ enum ipi_msg_type {
 	IPI_TIMER,
 	IPI_IRQ_WORK,
 	IPI_WAKEUP,
+	IPI_CALL_NMI_FUNC,
 	NR_IPI
 };
 
@@ -793,6 +794,7 @@ static const char *ipi_types[NR_IPI] __tracepoint_string = {
 	S(IPI_TIMER, "Timer broadcast interrupts"),
 	S(IPI_IRQ_WORK, "IRQ work interrupts"),
 	S(IPI_WAKEUP, "CPU wake-up interrupts"),
+	S(IPI_CALL_NMI_FUNC, "NMI function call interrupts"),
 };
 
 static void smp_cross_call(const struct cpumask *target, unsigned int ipinr);
@@ -840,6 +842,11 @@ void arch_irq_work_raise(void)
 }
 #endif
 
+void arch_send_call_nmi_func_ipi_mask(const struct cpumask *mask)
+{
+	smp_cross_call(mask, IPI_CALL_NMI_FUNC);
+}
+
 static void local_cpu_stop(void)
 {
 	set_cpu_online(smp_processor_id(), false);
@@ -932,6 +939,10 @@ static void do_handle_IPI(int ipinr)
 		break;
 #endif
 
+	case IPI_CALL_NMI_FUNC:
+		/* nop, IPI handlers for special features can be added here. */
+		break;
+
 	default:
 		pr_crit("CPU%u: Unknown IPI message 0x%x\n", cpu, ipinr);
 		break;
-- 
2.7.4