linux-kernel - [Patch v1 12/17] x86/apic: Only disable CPU x2apic mode when necessary

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Date:	Wed, 17 Dec 2014 12:35:43 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Joerg Roedel <joro@...tes.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>, x86@...nel.org,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Richard Weinberger <richard@....at>,
	Oren Twaig <oren@...lemp.com>
Cc:	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [Patch v1 12/17] 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@...ux.intel.com>
---
 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 c6204eab3d1b..95ed9e7e7548 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();
-- 
1.7.10.4

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