[PATCH 2/2] ACPI: irq: Prevent unregistering of GIC SGIs

[Marc Zyngier]

When using ACPI on arm64, which implies the GIC IRQ model, no
table should ever provide a GSI number in the range [0:15],
as these are reserved for IPIs.

However, drivers tend to call acpi_unregister_gsi() with any
random GSI number provided by half baked tables, which results
in an exploding kernel when its IPIs have been unconfigured.

In order to catch this, check for the silly case early, warn
that something is going wrong and avoid the above disaster.

Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
 drivers/acpi/irq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/irq.c b/drivers/acpi/irq.c
index e209081d644b..c68e694fca26 100644
--- a/drivers/acpi/irq.c
+++ b/drivers/acpi/irq.c
@@ -75,8 +75,12 @@ void acpi_unregister_gsi(u32 gsi)
 {
 	struct irq_domain *d = irq_find_matching_fwnode(acpi_gsi_domain_id,
 							DOMAIN_BUS_ANY);
-	int irq = irq_find_mapping(d, gsi);
+	int irq;
 
+	if (WARN_ON(acpi_irq_model == ACPI_IRQ_MODEL_GIC && gsi < 16))
+		return;
+
+	irq = irq_find_mapping(d, gsi);
 	irq_dispose_mapping(irq);
 }
 EXPORT_SYMBOL_GPL(acpi_unregister_gsi);
-- 
2.29.2