[RFC PATCH 14/36] arm64: interrupts: introduce generic interrupt masking helpers

[Vladimir Murzin]

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

As for the entry code, we want to replace `local_daif_...` helpers
so that they can properly handle both DAIF and PMR, as well controlling
their use more strongly.

Introduce new `local_all_irqs_...` helpers to replace them, which should
only be called in save/restore pairs.

Save the requested interrupt state as well, so we can check for
inconsistent interrupt masking in between save and restore.

There are two exceptions where it does not make sense to force
save/restore pairs for modifying the interrupt masks:
 - when initializing a CPU or
 - preparing to turn it off.

As we otherwise want to force save/restore pairs, those cases are
handled with specific helpers, making clear that they should not be
used outside of those cases, enforced with `CONFIG_DEBUG_IRQFLAGS`
enabled.

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 | 101 ++++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 arch/arm64/include/asm/interrupts/masking.h

diff --git a/arch/arm64/include/asm/interrupts/masking.h b/arch/arm64/include/asm/interrupts/masking.h
new file mode 100644
index 000000000000..66ee03f7ab68
--- /dev/null
+++ b/arch/arm64/include/asm/interrupts/masking.h
@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2025 Arm Ltd.
+ */
+#ifndef __ASM_INTERRUPTS_MASKING_H
+#define __ASM_INTERRUPTS_MASKING_H
+
+#include <asm/arch_gicv3.h>
+#include <asm/bug.h>
+#include <asm/cpufeature.h>
+#include <asm/interrupts/common_flags.h>
+#include <asm/ptrace.h>
+
+typedef struct arm64_exc_hwstates {
+	arm64_exc_hwstate_t saved;
+	arm64_exc_hwstate_t expected;
+} arm64_exc_hwstates_t;
+
+#ifdef CONFIG_DEBUG_IRQFLAGS
+/* Make sure the CPU init/tear down masking functions are only used once. */
+static DEFINE_PER_CPU(bool, irqs_masks_cpu_init_done);
+static DEFINE_PER_CPU(bool, irqs_masks_cpu_final_done);
+#endif
+
+static inline
+arm64_exc_hwstates_t local_all_irqs_save_mask(arm64_exc_context_t new)
+{
+	arm64_exc_hwstate_t state = arm64_exc_hwstate_of_context(new);
+	arm64_exc_hwstate_t actual = {.flags = arch_local_save_flags()};
+
+	if (IS_ENABLED(CONFIG_DEBUG_IRQFLAGS)) {
+		bool pnmi = system_uses_irq_prio_masking();
+
+		WARN_ON_ONCE(new < CRITICAL_CONTEXT &&
+			     actual.daif == DAIF_MASK);
+
+		WARN_ON_ONCE(new < ERROR_CONTEXT &&
+			     actual.daif == DAIF_ERRCTX);
+
+		WARN_ON_ONCE(new < NONMI_CONTEXT &&
+			     pnmi && actual.daif == DAIF_PROCCTX_NOIRQ);
+
+		WARN_ON_ONCE(new < NOIRQ_CONTEXT &&
+			     ((pnmi && actual.pmr == GIC_PRIO_IRQOFF) ||
+			      (!pnmi && actual.daif == DAIF_PROCCTX_NOIRQ)));
+	}
+
+	arm64_update_exc_hwstate(state, actual.pmr != state.pmr);
+
+	if (!arch_irqs_disabled_flags(actual.flags))
+		trace_hardirqs_off();
+
+	return (arm64_exc_hwstates_t){.saved = actual, .expected = state};
+}
+
+static inline void local_all_irqs_restore(arm64_exc_hwstates_t states)
+{
+	arm64_debug_exc_hwstate(states.expected);
+
+	if (!arch_irqs_disabled_flags(states.saved.flags))
+		trace_hardirqs_on();
+
+	arm64_update_exc_hwstate(states.saved, true);
+}
+
+#ifdef CONFIG_DEBUG_IRQFLAGS
+static inline
+void local_all_irqs_cpu_init_mask(arm64_exc_context_t context)
+{
+	WARN_ON(__this_cpu_read(irqs_masks_cpu_init_done));
+	if (context == PROCESS_CONTEXT)
+		trace_hardirqs_on();
+	arm64_update_exc_context(context, true);
+	__this_cpu_write(irqs_masks_cpu_init_done, true);
+	__this_cpu_write(irqs_masks_cpu_final_done, false);
+}
+
+static inline void local_all_irqs_final_mask(void)
+{
+	WARN_ON(__this_cpu_read(irqs_masks_cpu_final_done));
+	arm64_update_exc_context(CRITICAL_CONTEXT, true);
+	trace_hardirqs_off();
+	__this_cpu_write(irqs_masks_cpu_final_done, true);
+	__this_cpu_write(irqs_masks_cpu_init_done, false);
+}
+#else /* CONFIG_DEBUG_IRQFLAGS */
+static inline
+void local_all_irqs_cpu_init_mask(arm64_exc_context_t context)
+{
+	if (context == PROCESS_CONTEXT)
+		trace_hardirqs_on();
+	arm64_update_exc_context(context, true);
+}
+
+static inline void local_all_irqs_final_mask(void)
+{
+	arm64_update_exc_context(CRITICAL_CONTEXT, true);
+	trace_hardirqs_off();
+}
+#endif /* CONFIG_DEBUG_IRQFLAGS */
+#endif /* __ASM_INTERRUPTS_MASKING_H */
-- 
2.34.1