[PATCH 3/3] arm64: Avoid entering NMI context improperly

[Wei Li]

As the pseudo NMI can be enabled/disabled by cmdline parameter, the
arch_trigger_cpumask_backtrace() may still work through a normal IPI.

In this patch, we export the gic_supports_nmi() and add a check in
IPI_CPU_BACKTRACE process to avoid entering NMI context when pseudo
NMI is disabled.

Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
---
 arch/arm64/include/asm/arch_gicv3.h |  8 ++++++++
 arch/arm64/kernel/smp.c             | 14 ++++++++++++--
 drivers/irqchip/irq-gic-v3.c        |  8 +-------
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/arch_gicv3.h b/arch/arm64/include/asm/arch_gicv3.h
index 14b41ddc68ba..6655701ea7d4 100644
--- a/arch/arm64/include/asm/arch_gicv3.h
+++ b/arch/arm64/include/asm/arch_gicv3.h
@@ -156,6 +156,14 @@ static inline u32 gic_read_rpr(void)
 #define gits_write_vpendbaser(v, c)	writeq_relaxed(v, c)
 #define gits_read_vpendbaser(c)		readq_relaxed(c)
 
+extern struct static_key_false supports_pseudo_nmis;
+
+static inline bool gic_supports_nmi(void)
+{
+	return IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) &&
+	       static_branch_likely(&supports_pseudo_nmis);
+}
+
 static inline bool gic_prio_masking_enabled(void)
 {
 	return system_uses_irq_prio_masking();
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 7e862f9124f3..5550951527ea 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -950,9 +950,19 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
 #endif
 
 	case IPI_CPU_BACKTRACE:
-		nmi_enter();
+		if (gic_supports_nmi()) {
+			nmi_enter();
+		} else {
+			printk_nmi_enter();
+			irq_enter();
+		}
 		nmi_cpu_backtrace(regs);
-		nmi_exit();
+		if (gic_supports_nmi()) {
+			nmi_exit();
+		} else {
+			irq_exit();
+			printk_nmi_exit();
+		}
 		break;
 
 	default:
diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index 394aa5668dd6..b701727258b0 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -90,7 +90,7 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
  * For now, we only support pseudo-NMIs if we have non-secure view of
  * priorities.
  */
-static DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
+DEFINE_STATIC_KEY_FALSE(supports_pseudo_nmis);
 
 /* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
 static refcount_t ppi_nmi_refs[16];
@@ -261,12 +261,6 @@ static void gic_unmask_irq(struct irq_data *d)
 	gic_poke_irq(d, GICD_ISENABLER);
 }
 
-static inline bool gic_supports_nmi(void)
-{
-	return IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) &&
-	       static_branch_likely(&supports_pseudo_nmis);
-}
-
 static int gic_irq_set_irqchip_state(struct irq_data *d,
 				     enum irqchip_irq_state which, bool val)
 {
-- 
2.17.1