[PATCH] Do not reset apic to apic_noop with Xen

[M. Vefa Bicakci]

---
 arch/x86/include/asm/apic.h | 3 +++
 arch/x86/kernel/apic/apic.c | 7 +++++--
 arch/x86/xen/apic.c         | 4 +++-
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index b3d4c042e610..8c37580b7eb7 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -359,6 +359,9 @@ struct apic {
  */
 extern struct apic *apic;
 
+/* Indicates whether a hypervisor has already set 'apic'. */
+extern int apic_set_by_hypervisor;
+
 /*
  * APIC drivers are probed based on how they are listed in the .apicdrivers
  * section. So the order is important and enforced by the ordering
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 076c315cdf18..a3a1d4570acf 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -172,6 +172,8 @@ unsigned long mp_lapic_addr;
 int disable_apic;
 /* Disable local APIC timer from the kernel commandline or via dmi quirk */
 static int disable_apic_timer __initdata;
+/* Indicates whether a hypervisor has already set 'apic'. */
+int apic_set_by_hypervisor;
 /* Local APIC timer works in C2 */
 int local_apic_timer_c2_ok;
 EXPORT_SYMBOL_GPL(local_apic_timer_c2_ok);
@@ -1788,8 +1790,9 @@ void __init init_apic_mappings(void)
 		return;
 	}
 
-	/* If no local APIC can be found return early */
-	if (!smp_found_config && detect_init_APIC()) {
+	if (apic_set_by_hypervisor) {
+		/* Hypervisor has already taken care of the APIC. */
+	} else if (!smp_found_config && detect_init_APIC()) {
 		/* lets NOP'ify apic operations */
 		pr_info("APIC: disable apic facility\n");
 		apic_disable();
diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
index 5ac792a1d419..b79a003c13a5 100644
--- a/arch/x86/xen/apic.c
+++ b/arch/x86/xen/apic.c
@@ -229,8 +229,10 @@ void __init xen_init_apic(void)
 	x86_io_apic_ops.read = xen_io_apic_read;
 	/* On PV guests the APIC CPUID bit is disabled so none of the
 	 * routines end up executing. */
-	if (!xen_initial_domain())
+	if (!xen_initial_domain()) {
 		apic = &xen_pv_apic;
+		apic_set_by_hypervisor = 1;
+	}
 
 	x86_platform.apic_post_init = xen_apic_check;
 }
-- 
2.5.5