x86/IRQ: make fixup_irqs() skip unconnected internally used interrupts

Since the "Cannot set affinity ..." warning is a one time one, avoid
triggering it already at boot time when parking secondary threads and
the serial console uses a (still unconnected at that time) PCI IRQ.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2472,8 +2472,20 @@ void fixup_irqs(const cpumask_t *mask, b
         vector = irq_to_vector(irq);
         if ( vector >= FIRST_HIPRIORITY_VECTOR &&
              vector <= LAST_HIPRIORITY_VECTOR )
+        {
             cpumask_and(desc->arch.cpu_mask, desc->arch.cpu_mask, mask);
 
+            /*
+             * This can in particular happen when parking secondary threads
+             * during boot and when the serial console wants to use a PCI IRQ.
+             */
+            if ( desc->handler == &no_irq_type )
+            {
+                spin_unlock(&desc->lock);
+                continue;
+            }
+        }
+
         if ( desc->arch.move_cleanup_count )
         {
             /* The cleanup IPI may have got sent while we were still online. */