x86/apic: Only disable CPU x2apic mode when necessary

When interrupt remapping hardware is not in X2APIC, CPU X2APIC mode
will be disabled if:
1) Maximum CPU APIC ID is bigger than 255
2) hypervisior doesn't support x2apic mode.

But we should only check whether hypervisor supports X2APIC mode when
hypervisor(CONFIG_HYPERVISOR_GUEST) is enabled, otherwise X2APIC will
always be disabled when CONFIG_HYPERVISOR_GUEST is disabled and IR
doesn't work in X2APIC mode.
Signed-off-by: NJiang Liu <jiang.liu@linux.intel.com>
Tested-by: NJoerg Roedel <joro@8bytes.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: iommu@lists.linux-foundation.org
Cc: H. Peter Anvin <hpa@linux.intel.com>
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/1420615903-28253-12-git-send-email-jiang.liu@linux.intel.comSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/apic/apic.c

@@ -1601,7 +1601,8 @@ static __init void try_to_enable_x2apic(int ir_stat)
 		 * under KVM
 		 */
 		if (max_physical_apicid > 255 ||
-		    !hypervisor_x2apic_available()) {
+		    (IS_ENABLED(CONFIG_HYPERVISOR_GUEST) &&
+		     !hypervisor_x2apic_available())) {
 			pr_info("IRQ remapping doesn't support X2APIC mode, disable x2apic.\n");
 			if (x2apic_preenabled)
 				disable_x2apic();