[tip:x86/apic] x86/apic: Only disable CPU x2apic mode when necessary

[tip-bot for Jiang Liu <tipbot@zytor.com>]

Commit-ID:  5fcee53ce705d49c766f8a302c7e93bdfc33c124
Gitweb:     http://git.kernel.org/tip/5fcee53ce705d49c766f8a302c7e93bdfc33c124
Author:     Jiang Liu <jiang.liu@linux.intel.com>
AuthorDate: Wed, 7 Jan 2015 15:31:38 +0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 15 Jan 2015 11:24:23 +0100

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: Jiang Liu <jiang.liu@linux.intel.com>
Tested-by: Joerg 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.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/apic/apic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 04aec6b..2f16116 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/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();