[tip:x86/apic] x86: Skip cpus with apic-ids >= 255 in !x2apic_mode

[tip-bot for Suresh Siddha]

Commit-ID:  c284b42abadbb22083bfde24d308899c08d44ffa
Gitweb:     http://git.kernel.org/tip/c284b42abadbb22083bfde24d308899c08d44ffa
Author:     Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
AuthorDate: Wed, 21 Dec 2011 17:45:19 -0800
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Fri, 23 Dec 2011 11:01:49 -0800

x86: Skip cpus with apic-ids >= 255 in !x2apic_mode

If the x2apic mode is disabled for reasons like interrupt-remapping
not available etc, then we need to skip the logical cpu bringup of
apic-id's >= 255. Otherwise as the platform is in xapic mode, init/startup
IPI's will consider only the low 8-bits and there is a possibility of
re-sending init/startup IPI's to the logical cpu that is already online.

This will avoid potential reboots/unpredictable behavior etc.

Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20111222014632.702932458@xxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/smpboot.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 9f548cb..e38e217 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -840,7 +840,8 @@ int __cpuinit native_cpu_up(unsigned int cpu)
 	pr_debug("++++++++++++++++++++=_---CPU UP  %u\n", cpu);
 
 	if (apicid == BAD_APICID || apicid == boot_cpu_physical_apicid ||
-	    !physid_isset(apicid, phys_cpu_present_map)) {
+	    !physid_isset(apicid, phys_cpu_present_map) ||
+	    (!x2apic_mode && apicid >= 255)) {
 		printk(KERN_ERR "%s: bad cpu %d\n", __func__, cpu);
 		return -EINVAL;
 	}
--
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