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@hp.com>
Link: http://lkml.kernel.org/r/20110712055831.2498.78521.sendpatchset@nchumbalkar.americas.cpqcorp.net
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b9338b8..f7b0c7a 100644 (file)
--- 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 */