[PATCH v6 7/7] arm64: kgdb: Roundup cpus using IPI as NMI

[Sumit Garg <sumit.garg@linaro.org>]

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

So instead switch to roundup CPUs using IPI turned as NMI. And in
case a particular arm64 platform doesn't supports pseudo NMIs,
it will switch back to default kgdb CPUs roundup mechanism.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
---
 arch/arm64/include/asm/kgdb.h |  9 +++++++++
 arch/arm64/kernel/ipi_nmi.c   |  5 +++++
 arch/arm64/kernel/kgdb.c      | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/arch/arm64/include/asm/kgdb.h b/arch/arm64/include/asm/kgdb.h
index 21fc85e..c3d2425 100644
--- a/arch/arm64/include/asm/kgdb.h
+++ b/arch/arm64/include/asm/kgdb.h
@@ -24,6 +24,15 @@ static inline void arch_kgdb_breakpoint(void)
 extern void kgdb_handle_bus_error(void);
 extern int kgdb_fault_expected;
 
+#ifdef CONFIG_KGDB
+extern bool kgdb_ipi_nmicallback(int cpu, void *regs);
+#else
+static inline bool kgdb_ipi_nmicallback(int cpu, void *regs)
+{
+	return false;
+}
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 /*
diff --git a/arch/arm64/kernel/ipi_nmi.c b/arch/arm64/kernel/ipi_nmi.c
index 597dcf7..6ace182 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/nmi.h>
 #include <linux/smp.h>
 
@@ -45,10 +46,14 @@ bool arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
 static irqreturn_t ipi_nmi_handler(int irq, void *data)
 {
 	irqreturn_t ret = IRQ_NONE;
+	unsigned int cpu = smp_processor_id();
 
 	if (nmi_cpu_backtrace(get_irq_regs()))
 		ret = IRQ_HANDLED;
 
+	if (kgdb_ipi_nmicallback(cpu, get_irq_regs()))
+		ret = IRQ_HANDLED;
+
 	return ret;
 }
 
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c
index 1a157ca3..c26e710 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 +354,37 @@ int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
 	return aarch64_insn_write((void *)bpt->bpt_addr,
 			*(u32 *)bpt->saved_instr);
 }
+
+bool kgdb_ipi_nmicallback(int cpu, void *regs)
+{
+	if (atomic_read(&kgdb_active) != -1) {
+		kgdb_nmicallback(cpu, regs);
+		return true;
+	}
+
+	return false;
+}
+
+static void kgdb_smp_callback(void *data)
+{
+	unsigned int cpu = smp_processor_id();
+
+	if (atomic_read(&kgdb_active) != -1)
+		kgdb_nmicallback(cpu, get_irq_regs());
+}
+
+bool kgdb_arch_roundup_cpus(void)
+{
+	struct cpumask mask;
+
+	if (!arm64_supports_nmi())
+		return false;
+
+	cpumask_copy(&mask, cpu_online_mask);
+	cpumask_clear_cpu(raw_smp_processor_id(), &mask);
+	if (cpumask_empty(&mask))
+		return false;
+
+	arm64_send_nmi(&mask);
+	return true;
+}
-- 
2.7.4