x86/apic: Mark single target interrupts

If the interrupt destination mode of the APIC is physical then the
effective affinity is restricted to a single CPU.

Mark the interrupt accordingly in the domain allocation code, so the core
code can avoid pointless affinity setting attempts.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235447.508846202@linutronix.de

arch/x86/kernel/apic/vector.c

@@ -371,6 +371,13 @@ static int x86_vector_alloc_irqs(struct irq_domain *domain, unsigned int virq,
 					       irq_data);
 		if (err)
 			goto error;
+		/*
+		 * If the apic destination mode is physical, then the
+		 * effective affinity is restricted to a single target
+		 * CPU. Mark the interrupt accordingly.
+		 */
+		if (!apic->irq_dest_mode)
+			irqd_set_single_target(irq_data);
 	}
 
 	return 0;