linux-kernel - [tip:x86/apic] x86, x2apic: Preserve high 32-bits of IA32_APIC

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Date:	Wed, 13 Jul 2011 03:06:56 GMT
From:	tip-bot for Naga Chumbalkar <nagananda.chumbalkar@...com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	gorcunov@...nvz.org, suresh.b.siddha@...el.com,
	nagananda.chumbalkar@...com, tglx@...utronix.de,
	hpa@...ux.intel.com
Subject: [tip:x86/apic] x86, x2apic: Preserve high 32-bits of IA32_APIC_BASE MSR

Commit-ID:  25970852280c9d5fb2de899769880d3e97332baa
Gitweb:     http://git.kernel.org/tip/25970852280c9d5fb2de899769880d3e97332baa
Author:     Naga Chumbalkar <nagananda.chumbalkar@...com>
AuthorDate: Tue, 12 Jul 2011 05:59:07 +0000
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Tue, 12 Jul 2011 14:33:49 -0700

x86, x2apic: Preserve high 32-bits of IA32_APIC_BASE MSR

If there's no special reason to zero-out the "high" 32-bits of the IA32_APIC_BASE
MSR, let's preserve it.

The x2APIC Specification doesn't explicitly state any such requirement. (Sec 2.2
in: http://www.intel.com/Assets/PDF/manual/318148.pdf).

Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@...com>
Link: http://lkml.kernel.org/r/20110712055831.2498.78521.sendpatchset@nchumbalkar.americas.cpqcorp.net
Reviewed-by: Cyrill Gorcunov <gorcunov@...nvz.org>
Reviewed-by: Suresh Siddha <suresh.b.siddha@...el.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/kernel/apic/apic.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b9338b8..f7b0c7a 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1429,7 +1429,7 @@ void enable_x2apic(void)
 	rdmsr(MSR_IA32_APICBASE, msr, msr2);
 	if (!(msr & X2APIC_ENABLE)) {
 		printk_once(KERN_INFO "Enabling x2apic\n");
-		wrmsr(MSR_IA32_APICBASE, msr | X2APIC_ENABLE, 0);
+		wrmsr(MSR_IA32_APICBASE, msr | X2APIC_ENABLE, msr2);
 	}
 }
 #endif /* CONFIG_X86_X2APIC */
--
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