irq: add a (temporary) CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY

Going forward we want architecture/entry code to perform all the
necessary work to enter/exit IRQ context, with irqchip code merely
handling the mapping of the interrupt to any handler(s). Among other
reasons, this is necessary to consistently fix some longstanding issues
with the ordering of lockdep/RCU/tracing instrumentation which many
architectures get wrong today in their entry code.

Importantly, rcu_irq_{enter,exit}() must be called precisely once per
IRQ exception, so that rcu_is_cpu_rrupt_from_idle() can correctly
identify when an interrupt was taken from an idle context which must be
explicitly preempted. Currently handle_domain_irq() calls
rcu_irq_{enter,exit}() via irq_{enter,exit}(), but entry code needs to
be able to call rcu_irq_{enter,exit}() earlier for correct ordering
across lockdep/RCU/tracing updates for sequences such as:

  lockdep_hardirqs_off(CALLER_ADDR0);
  rcu_irq_enter();
  trace_hardirqs_off_finish();

To permit each architecture to be converted to the new style in turn,
this patch adds a new CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY selected by all
current users of HANDLE_DOMAIN_IRQ, which gates the existing behaviour.
When CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY is not selected,
handle_domain_irq() requires entry code to perform the
irq_{enter,exit}() work, with an explicit check for this matching the
style of handle_domain_nmi().

Subsequent patches will:

1) Add the necessary IRQ entry accounting to each architecture in turn,
   dropping CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY from that architecture's
   Kconfig.

2) Remove CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY once it is no longer
   selected.

3) Convert irqchip drivers to consistently use
   generic_handle_domain_irq() rather than handle_domain_irq().

4) Remove handle_domain_irq() and CONFIG_HANDLE_DOMAIN_IRQ.

... which should leave us with a clear split of responsiblity across the
entry and irqchip code, making it possible to perform additional
cleanups and fixes for the aforementioned longstanding issues with entry
code.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 34 insertions, 0 deletions

diff --git a/kernel/irq/Kconfig b/kernel/irq/Kconfig
index fbc54c2a7f23..897dfc552bb0 100644
--- a/kernel/irq/Kconfig
+++ b/kernel/irq/Kconfig
@@ -100,6 +100,10 @@ config IRQ_MSI_IOMMU
 config HANDLE_DOMAIN_IRQ
 	bool
 
+# Legacy behaviour; architectures should call irq_{enter,exit}() themselves
+config HANDLE_DOMAIN_IRQ_IRQENTRY
+	bool
+
 config IRQ_TIMINGS
 	bool
 
diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
index e25d4bddf3d8..5677a849cf1f 100644
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -676,6 +676,7 @@ int generic_handle_domain_irq(struct irq_domain *domain, unsigned int hwirq)
 EXPORT_SYMBOL_GPL(generic_handle_domain_irq);
 
 #ifdef CONFIG_HANDLE_DOMAIN_IRQ
+#ifdef CONFIG_HANDLE_DOMAIN_IRQ_IRQENTRY
 /**
  * handle_domain_irq - Invoke the handler for a HW irq belonging to a domain,
  *                     usually for a root interrupt controller
@@ -699,6 +700,35 @@ int handle_domain_irq(struct irq_domain *domain,
 	set_irq_regs(old_regs);
 	return ret;
 }
+#else
+/**
+ * handle_domain_irq - Invoke the handler for a HW irq belonging to a domain,
+ *                     usually for a root interrupt controller
+ * @domain:	The domain where to perform the lookup
+ * @hwirq:	The HW irq number to convert to a logical one
+ * @regs:	Register file coming from the low-level handling code
+ *
+ * 		This function must be called from an IRQ context.
+ *
+ * Returns:	0 on success, or -EINVAL if conversion has failed
+ */
+int handle_domain_irq(struct irq_domain *domain,
+		      unsigned int hwirq, struct pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+	int ret;
+
+	/*
+	 * IRQ context needs to be setup earlier.
+	 */
+	WARN_ON(!in_irq());
+
+	ret = generic_handle_domain_irq(domain, hwirq);
+
+	set_irq_regs(old_regs);
+	return ret;
+}
+#endif
 
 /**
  * handle_domain_nmi - Invoke the handler for a HW irq belonging to a domain