[PATCH RFC v3 27/30] ARM: irq: Add irqstack helpers

[Linus Walleij <linus.walleij@linaro.org>]

Add two helpers that essentially re-implement some IRQ
dispatch code in C: on_irq_stack() that checks if a regs
context is on the IRQ stack, and call_on_irq_stack()
so we can explicitly issue handle_irq() on the IRQ
stack from a C program.

Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 arch/arm/kernel/irq.c | 31 +++++++++++++++++++++++++++++++
 arch/arm/kernel/irq.h |  3 +++
 2 files changed, 34 insertions(+)

diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index e1993e28a9ecfd80b55b2677253ac582467e6c14..4c1a678b72b326e42c871b994c09d1fa4b0863f6 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -43,6 +43,7 @@
 #include <asm/mach/irq.h>
 #include <asm/mach/time.h>
 
+#include "irq.h"
 #include "reboot.h"
 
 unsigned long irq_err_count;
@@ -71,6 +72,36 @@ static void __init init_irq_stacks(void)
 	}
 }
 
+/*
+ * on_irq_stack() - check if a regs context is using the IRQ stack
+ * @regs: the context to check
+ * Returns true if regs is using the IRQ stack
+ */
+bool on_irq_stack(struct pt_regs *regs)
+{
+	u8 *high = __this_cpu_read(irq_stack_ptr);
+	u8 *low = high - THREAD_SIZE;
+	u8 *sp = (u8 *)regs->ARM_sp;
+	bool on_stack;
+
+	on_stack = (low <= sp && sp <= high);
+
+	if (on_stack && IS_ENABLED(CONFIG_VMAP_STACK))
+		/*
+		 * Also check that SP is inside the linear kernel memory
+		 * if using VMAP:ed stacks.
+		 * TODO: Ask Ard to explain why we need to do this
+		 */
+		on_stack = (sp > (u8 *)high_memory);
+
+	return on_stack;
+}
+
+void call_on_irq_stack(void (*fn)(void *), void *arg)
+{
+	call_with_stack(fn, arg, __this_cpu_read(irq_stack_ptr));
+}
+
 #ifdef CONFIG_SOFTIRQ_ON_OWN_STACK
 static void ____do_softirq(void *arg)
 {
diff --git a/arch/arm/kernel/irq.h b/arch/arm/kernel/irq.h
new file mode 100644
index 0000000000000000000000000000000000000000..c5186b67242a2976fe702154ed4f2a22eca51add
--- /dev/null
+++ b/arch/arm/kernel/irq.h
@@ -0,0 +1,3 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+bool on_irq_stack(struct pt_regs *regs);
+void call_on_irq_stack(void (*fn)(void *), void *arg);

-- 
2.47.1