[PATCH v2 4/5] arm64: irqflags: Introduce explicit debugging for IRQ priorities

[Julien Thierry]

Using IRQ priority masking to enable/disable interrupts is a bit
sensitive as it requires to deal with both ICC_PMR_EL1 and PSR.I.

Introduce some validity checks to both highlight the states in which
functions dealing with IRQ enabling/disabling can (not) be called, and
bark a warning when called in an unexpected state.

Since these checks are done on hotpaths, introduce a build option to
choose whether to do the checking.

Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
---
 arch/arm64/Kconfig                 | 11 +++++++++++
 arch/arm64/include/asm/daifflags.h |  9 +++++++++
 arch/arm64/include/asm/irqflags.h  | 14 ++++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7e34b9e..3fb38f3 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1359,6 +1359,17 @@ config ARM64_PSEUDO_NMI

 	  If unsure, say N

+if ARM64_PSEUDO_NMI
+config ARM64_DEBUG_PRIORITY_MASKING
+	bool "Debug interrupt priority masking"
+	help
+	  This adds runtime checks to functions enabling/disabling
+	  interrupts when using priority masking. The additional checks verify
+	  the validity of ICC_PMR_EL1 when calling concerned functions.
+
+	  If unsure, say N
+endif
+
 config RELOCATABLE
 	bool
 	help
diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index a32ece9..9512968 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -28,6 +28,11 @@
 /* mask/save/unmask/restore all exceptions, including interrupts. */
 static inline void local_daif_mask(void)
 {
+	WARN_ON(IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING) &&
+		system_uses_irq_prio_masking() &&
+		(read_sysreg_s(SYS_ICC_PMR_EL1) == (GIC_PRIO_IRQOFF |
+						    GIC_PRIO_IGNORE_PMR)));
+
 	asm volatile(
 		"msr	daifset, #0xf		// local_daif_mask\n"
 		:
@@ -62,6 +67,10 @@ static inline void local_daif_restore(unsigned long flags)
 {
 	bool irq_disabled = flags & PSR_I_BIT;

+	WARN_ON(IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING) &&
+		system_uses_irq_prio_masking() &&
+		!(read_sysreg(daif) & PSR_I_BIT));
+
 	if (!irq_disabled) {
 		trace_hardirqs_on();

diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
index 516cdfc..a40abc2 100644
--- a/arch/arm64/include/asm/irqflags.h
+++ b/arch/arm64/include/asm/irqflags.h
@@ -40,6 +40,13 @@
  */
 static inline void arch_local_irq_enable(void)
 {
+	if (IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING) &&
+	    system_uses_irq_prio_masking()) {
+		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
+
+		WARN_ON(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
+	}
+
 	asm volatile(ALTERNATIVE(
 		"msr	daifclr, #2		// arch_local_irq_enable\n"
 		"nop",
@@ -53,6 +60,13 @@ static inline void arch_local_irq_enable(void)

 static inline void arch_local_irq_disable(void)
 {
+	if (IS_ENABLED(CONFIG_ARM64_DEBUG_PRIORITY_MASKING) &&
+	    system_uses_irq_prio_masking()) {
+		u32 pmr = read_sysreg_s(SYS_ICC_PMR_EL1);
+
+		WARN_ON(pmr != GIC_PRIO_IRQON && pmr != GIC_PRIO_IRQOFF);
+	}
+
 	asm volatile(ALTERNATIVE(
 		"msr	daifset, #2		// arch_local_irq_disable",
 		"msr_s  " __stringify(SYS_ICC_PMR_EL1) ", %0",
--
1.9.1