[tip:x86/urgent] x86, apic: Don't use logical-flat mode when CPU hotplug may exceed 8 CPUs

[tip-bot for Suresh Siddha <suresh.b.siddha@intel.com>]

Commit-ID:  418f727639cfc8f03068aae09f473c493c759b9b
Gitweb:     http://git.kernel.org/tip/418f727639cfc8f03068aae09f473c493c759b9b
Author:     Suresh Siddha <suresh.b.siddha@intel.com>
AuthorDate: Tue, 9 Feb 2010 09:18:35 -0800
Committer:  H. Peter Anvin <hpa@zytor.com>
CommitDate: Tue, 9 Feb 2010 09:29:17 -0800

x86, apic: Don't use logical-flat mode when CPU hotplug may exceed 8 CPUs

We need to fall back from logical-flat APIC mode to physical-flat mode
when we have more than 8 CPUs.  However, in the presence of CPU
hotplug, we have to consider the number of possible CPUs rather than
the number of current CPUs; otherwise we may cross the 8-CPU boundary
when CPUs are added later.

Reported-by: Shaohui Zheng <shaohui.zheng@intel.com>
Acked-by: Shaohui Zheng <shaohui.zheng@intel.com>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <20100118201256.672679042@sbs-t61.sc.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: <stable@kernel.org>
---
 arch/x86/kernel/apic/apic.c     |    2 +-
 arch/x86/kernel/apic/probe_64.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 3987e44..fc1d579 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1892,7 +1892,7 @@ void __cpuinit generic_processor_info(int apicid, int version)
 		max_physical_apicid = apicid;
 
 #ifdef CONFIG_X86_32
-	if (num_processors > 8) {
+	if (num_possible_cpus() > 8) {
 		switch (boot_cpu_data.x86_vendor) {
 		case X86_VENDOR_INTEL:
 			if (!APIC_XAPIC(version)) {
diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
index 450fe20..83e9be4 100644
--- a/arch/x86/kernel/apic/probe_64.c
+++ b/arch/x86/kernel/apic/probe_64.c
@@ -67,7 +67,7 @@ void __init default_setup_apic_routing(void)
 	}
 #endif
 
-	if (apic == &apic_flat && num_processors > 8)
+	if (apic == &apic_flat && num_possible_cpus() > 8)
 			apic = &apic_physflat;
 
 	printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);