x86/apic: Handle XAPIC remap mode proper.

If remapping is in XAPIC mode, the setup code just skips X2APIC
initialization without checking max CPU APIC ID in system, which may
cause problem if system has a CPU with APIC ID bigger than 255.

Handle IR in XAPIC mode the same way as if remapping is disabled.

[ tglx: Split out from previous patch ]
Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: iommu@lists.linux-foundation.org
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Rientjes <rientjes@google.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Oren Twaig <oren@scalemp.com>
Link: http://lkml.kernel.org/r/1420615903-28253-8-git-send-email-jiang.liu@linux.intel.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/apic/apic.c

@@ -1596,7 +1596,7 @@ static __init void try_to_enable_x2apic(int ir_stat)
 	if (!x2apic_supported())
 		return;
 
-	if (ir_stat < 0) {
+	if (ir_stat != IRQ_REMAP_X2APIC_MODE) {
 		/* IR is required if there is APIC ID > 255 even when running
 		 * under KVM
 		 */
@@ -1613,10 +1613,6 @@ static __init void try_to_enable_x2apic(int ir_stat)
 		 * only in physical mode
 		 */
 		x2apic_force_phys();
-
-	} else if (ir_stat == IRQ_REMAP_XAPIC_MODE) {
-		pr_info("x2apic not enabled, IRQ remapping is in xapic mode\n");
-		return;
 	}
 
 	if (!x2apic_mode) {