--- arch/i386/kernel/apic.c.orig	2004-10-04 14:54:27.000000000 +0200
+++ arch/i386/kernel/apic.c	2004-10-04 14:56:20.000000000 +0200
@@ -269,6 +269,9 @@ int __init verify_local_APIC(void)
 
 void __init sync_Arb_IDs(void)
 {
+	/* Unsupported on P4 - see Intel Dev. Manual Vol. 3, Ch. 8.6.1 */
+	if (boot_cpu_data.x86 == 15)
+		return;
 	/*
 	 * Wait for idle.
 	 */