[PATCH] genirq/msi: Shutdown managed interrupts with unsatifiable affinities

[Marc Zyngier]

When booting with maxcpus=<small number>, interrupt controllers
such as the GICv3 ITS may not be able to satisfy the affinity of
some managed interrupts, as some of the HW resources are simply
not available.

In order to deal with this, do not try to activate such interrupt
if there is no online CPU capable of handling it. Instead, place
it in shutdown state. Once a capable CPU shows up, it will be
activated.

Reported-by: John Garry <john.garry@xxxxxxxxxx>
Reported-by: David Decotigny <ddecotig@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
 kernel/irq/msi.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index 2bdfce5edafd..aa84ce84c2ec 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -818,6 +818,18 @@ static int msi_init_virq(struct irq_domain *domain, int virq, unsigned int vflag
 		irqd_clr_can_reserve(irqd);
 		if (vflags & VIRQ_NOMASK_QUIRK)
 			irqd_set_msi_nomask_quirk(irqd);
+
+		/*
+		 * If the interrupt is managed but no CPU is available
+		 * to service it, shut it down until better times.
+		 */
+		if ((vflags & VIRQ_ACTIVATE) &&
+		    irqd_affinity_is_managed(irqd) &&
+		    !cpumask_intersects(irq_data_get_affinity_mask(irqd),
+					cpu_online_mask)) {
+			    irqd_set_managed_shutdown(irqd);
+			    return 0;
+		    }
 	}
 
 	if (!(vflags & VIRQ_ACTIVATE))
-- 
2.30.2