Do not enforce unique IO_APIC_ID for Xeon processors in EM64T mode (x86_64)

diff -puN arch/x86_64/kernel/setup.c~no-ioapic-check-x86_64 arch/x86_64/kernel/setup.c
@@ -346,6 +346,9 @@ static __init void parse_cmdline_early (
 			ioapic_force = 1;
 		}
 			
+		if (!memcmp(from, "ioapic_id_check=", 16))
+			ioapic_id_check_setup(from+16);
+
 		if (!memcmp(from, "mem=", 4))
 			parse_memopt(from+4, &from); 
 

@@ -547,6 +550,9 @@ void __init setup_arch(char **cmdline_p)
 	data_resource.start = virt_to_phys(&_etext);
 	data_resource.end = virt_to_phys(&_edata)-1;
 
+#ifdef CONFIG_NO_IOAPIC_CHECK
+	skip_ioapic_id_check = 1;
+#endif
 	parse_cmdline_early(cmdline_p);
 
 	early_identify_cpu(&boot_cpu_data);

diff -puN arch/x86_64/kernel/io_apic.c~no-ioapic-check-x86_64 arch/x86_64/kernel/io_apic.c
@@ -216,6 +216,7 @@ static void clear_IO_APIC (void)
 static int pirq_entries [MAX_PIRQS];
 static int pirqs_enabled;
 int skip_ioapic_setup;
+int skip_ioapic_id_check;
 int ioapic_force;
 
 /* dummy parsing: see setup.c */

@@ -233,8 +234,19 @@ static int __init enable_ioapic_setup(ch
 	return 1;
 }
 
+int __init ioapic_id_check_setup(char *str)
+{
+	if (!strncmp(str, "on", 2)) {
+		skip_ioapic_id_check = 0;
+	} else if (!strncmp(str, "off", 3)) {
+		skip_ioapic_id_check = 1;
+	}
+	return 1;
+}
+
 __setup("noapic", disable_ioapic_setup);
 __setup("apic", enable_ioapic_setup);
+__setup("ioapic_id_check=", ioapic_id_check_setup);
 
 #include <asm/pci-direct.h>
 #include <linux/pci_ids.h>

@@ -1867,12 +1879,15 @@ int __init io_apic_get_unique_id (int io
 	int i = 0;
 
 	/*
+	 * P4-class systems take advantage of APIC system bus architecture.
+	 */
+
+	if (skip_ioapic_id_check)
+		return apic_id;
+	/*
 	 * The P4 platform supports up to 256 APIC IDs on two separate APIC 
 	 * buses (one for LAPICs, one for IOAPICs), where predecessors only 
 	 * supports up to 16 on one shared APIC bus.
-	 * 
-	 * TBD: Expand LAPIC/IOAPIC support on P4-class systems to take full
-	 *      advantage of new APIC bus architecture.
 	 */
 
 	if (physids_empty(apic_id_map))

diff -puN include/asm-x86_64/io_apic.h~no-ioapic-check-x86_64 include/asm-x86_64/io_apic.h
@@ -195,6 +195,9 @@ static inline void io_apic_sync(unsigned
 /* 1 if "noapic" boot option passed */
 extern int skip_ioapic_setup;
 
+/* 1 if "ioapic_id_check=off" boot option passed */
+extern int skip_ioapic_id_check;
+
 /*
  * If we use the IO-APIC for IRQ routing, disable automatic
  * assignment of PCI IRQ's.

diff -puN include/asm-x86_64/proto.h~no-ioapic-check-x86_64 include/asm-x86_64/proto.h
@@ -75,6 +75,7 @@ extern void syscall32_cpu_init(void);
 extern void setup_node_bootmem(int nodeid, unsigned long start, unsigned long end);
 
 extern void check_ioapic(void);
+extern int ioapic_id_check_setup(char *str);
 extern void check_efer(void);
 
 extern int unhandled_signal(struct task_struct *tsk, int sig);

@@ -93,6 +94,7 @@ extern int disable_apic;
 extern unsigned cpu_khz;
 extern int ioapic_force;
 extern int skip_ioapic_setup;
+extern int extern int skip_ioapic_id_check;
 extern int acpi_ht;
 extern int acpi_disabled;