x86/irq: Hide 'HYP:' line in /proc/interrupts when not on Xen/Hyper-V

Hypervisor callback interrupts are only accounted on
Xen/Hyper-V. There is no point in having always-zero HYP: line
on other hypervisors or bare metal. Print the line only if
HYPERVISOR_CALLBACK_VECTOR was allocated.

Reported-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Andrew Jones <drjones@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1436286373-11908-1-git-send-email-vkuznets@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/irq.c

@@ -139,10 +139,13 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 	seq_puts(p, "  Machine check polls\n");
 #endif
 #if IS_ENABLED(CONFIG_HYPERV) || defined(CONFIG_XEN)
-	seq_printf(p, "%*s: ", prec, "HYP");
-	for_each_online_cpu(j)
-		seq_printf(p, "%10u ", irq_stats(j)->irq_hv_callback_count);
-	seq_puts(p, "  Hypervisor callback interrupts\n");
+	if (test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors)) {
+		seq_printf(p, "%*s: ", prec, "HYP");
+		for_each_online_cpu(j)
+			seq_printf(p, "%10u ",
+				   irq_stats(j)->irq_hv_callback_count);
+		seq_puts(p, "  Hypervisor callback interrupts\n");
+	}
 #endif
 	seq_printf(p, "%*s: %10u\n", prec, "ERR", atomic_read(&irq_err_count));
 #if defined(CONFIG_X86_IO_APIC)