[RFC PATCH v2 17/45] arm64: interrupts: introduce a helper for GIC priority initialization

[Vladimir Murzin]

From: Ada Couprie Diaz <ada.coupriediaz at arm.com>

Arm64's `init_IRQ()` calls `local_daif_restore()` to synchronize
interrupt masking via DAIF and switch to masking via PMR.  This
depends on a very specific behaviour of `local_daif_restore()` which
will clear DAIF if masking interrupts via PMR, which will get removed
in the future.

As `setup_arch()` cleared DA only earlier, introduce a dedicated
helper that explicitly initializes the PMR to mask interrupts and
clears DAIF, switching to IRQ priority masking.

Given it is a dedicated helper, add a lockdep assertion as
`setup_arch()` should always have called `trace_hardirqs_off()` when
clearing DA, otherwise something bad happened.

Signed-off-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
---
 arch/arm64/include/asm/interrupts/masking.h | 19 +++++++++++++++++++
 arch/arm64/kernel/irq.c                     | 13 +++++--------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/interrupts/masking.h b/arch/arm64/include/asm/interrupts/masking.h
index fd4fb5497c7e..193089fda252 100644
--- a/arch/arm64/include/asm/interrupts/masking.h
+++ b/arch/arm64/include/asm/interrupts/masking.h
@@ -5,6 +5,8 @@
 #ifndef __ASM_INTERRUPTS_MASKING_H
 #define __ASM_INTERRUPTS_MASKING_H
 
+#include <linux/lockdep.h>
+
 #include <asm/arch_gicv3.h>
 #include <asm/bug.h>
 #include <asm/cpufeature.h>
@@ -86,4 +88,21 @@ static inline void local_exceptions_final_mask(void)
 	__local_exceptions_final_mask();
 }
 #endif /* CONFIG_DEBUG_IRQFLAGS */
+
+/*
+ * During early boot, we unmask PSR.DA before the GIC has been set up.
+ * If we use IRQ priority masking, the PMR and PSR will be out of sync
+ * after the GIC is enabled : sync them up.
+ */
+static inline void local_interrupt_priority_init(void)
+{
+	if (!system_uses_irq_prio_masking())
+		return;
+
+	WARN_ON(read_sysreg(daif) & PSR_A_BIT);
+	lockdep_assert_irqs_disabled();
+
+	arm64_update_exc_context(NOIRQ_CONTEXT);
+}
+
 #endif /* __ASM_INTERRUPTS_MASKING_H */
diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
index ca98db345f92..a3d9128ba195 100644
--- a/arch/arm64/kernel/irq.c
+++ b/arch/arm64/kernel/irq.c
@@ -130,14 +130,11 @@ void __init init_IRQ(void)
 
 	irqchip_init();
 
-	if (system_uses_irq_prio_masking()) {
-		/*
-		 * Now that we have a stack for our IRQ handler, set
-		 * the PMR/PSR pair to a consistent state.
-		 */
-		WARN_ON(read_sysreg(daif) & PSR_A_BIT);
-		local_daif_restore(DAIF_PROCCTX_NOIRQ);
-	}
+	/*
+	 * Now that we have a stack for our IRQ handler,
+	 * let's mask interrupts via the PMR.
+	 */
+	local_interrupt_priority_init();
 }
 
 #ifdef CONFIG_DEBUG_IRQFLAGS
-- 
2.34.1