[PATCH v4 4/5] arm64: kgdb: Round up cpus using IPI as NMI

[Sumit Garg]

arm64 platforms with GICv3 or later supports pseudo NMIs which can be
leveraged to round up CPUs which are stuck in hard lockup state with
interrupts disabled that wouldn't be possible with a normal IPI.

So instead switch to round up CPUs using IPI turned as NMI. And in
case a particular arm64 platform doesn't supports pseudo NMIs,
this IPI will act as a normal IPI which maintains existing kgdb
functionality.

Signed-off-by: Sumit Garg <sumit.garg at linaro.org>
---
 arch/arm64/include/asm/kgdb.h |  8 ++++++++
 arch/arm64/kernel/ipi_nmi.c   |  5 ++++-
 arch/arm64/kernel/kgdb.c      | 21 +++++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kgdb.h b/arch/arm64/include/asm/kgdb.h
index 21fc85e..6f3d3af 100644
--- a/arch/arm64/include/asm/kgdb.h
+++ b/arch/arm64/include/asm/kgdb.h
@@ -24,6 +24,14 @@ static inline void arch_kgdb_breakpoint(void)
 extern void kgdb_handle_bus_error(void);
 extern int kgdb_fault_expected;
 
+#ifdef CONFIG_KGDB
+extern void ipi_kgdb_nmicallback(int cpu, void *regs);
+#else
+static inline void ipi_kgdb_nmicallback(int cpu, void *regs)
+{
+}
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 /*
diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
index 355ef92..627bc11 100644
--- a/arch/arm64/kernel/ipi_nmi.c
+++ b/arch/arm64/kernel/ipi_nmi.c
@@ -8,6 +8,7 @@
 
 #include <linux/interrupt.h>
 #include <linux/irq.h>
+#include <linux/kgdb.h>
 #include <linux/smp.h>
 
 #include <asm/nmi.h>
@@ -26,7 +27,9 @@ void arch_send_call_nmi_func_ipi_mask(cpumask_t *mask)
 
 static irqreturn_t ipi_nmi_handler(int irq, void *data)
 {
-	/* nop, NMI handlers for special features can be added here. */
+	unsigned int cpu = smp_processor_id();
+
+	ipi_kgdb_nmicallback(cpu, get_irq_regs());
 
 	return IRQ_HANDLED;
 }
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index 1a157ca3..0991275 100644
--- a/arch/arm64/kernel/kgdb.c
+++ b/arch/arm64/kernel/kgdb.c
@@ -17,6 +17,7 @@
 
 #include <asm/debug-monitors.h>
 #include <asm/insn.h>
+#include <asm/nmi.h>
 #include <asm/traps.h>
 
 struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] = {
@@ -353,3 +354,23 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 	return aarch64_insn_write((void *)bpt->bpt_addr,
 			*(u32 *)bpt->saved_instr);
 }
+
+void ipi_kgdb_nmicallback(int cpu, void *regs)
+{
+	if (atomic_read(&kgdb_active) != -1)
+		kgdb_nmicallback(cpu, regs);
+}
+
+#ifdef CONFIG_SMP
+void kgdb_roundup_cpus(void)
+{
+	struct cpumask mask;
+
+	cpumask_copy(&mask, cpu_online_mask);
+	cpumask_clear_cpu(raw_smp_processor_id(), &mask);
+	if (cpumask_empty(&mask))
+		return;
+
+	arch_send_call_nmi_func_ipi_mask(&mask);
+}
+#endif
-- 
2.7.4