[tip:x86/apic] x86/smpboot: Check APIC ID before setting up default routing

[tip-bot for Wei Jiangang]

Commit-ID:  384d9fe3741657c8ed8cd9bf30bc1d4611864d56
Gitweb:     http://git.kernel.org/tip/384d9fe3741657c8ed8cd9bf30bc1d4611864d56
Author:     Wei Jiangang <weijg.fnst@xxxxxxxxxxxxxx>
AuthorDate: Fri, 19 Aug 2016 11:22:36 +0800
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 24 Aug 2016 11:24:33 +0200

x86/smpboot: Check APIC ID before setting up default routing

This is not a bugfix, but code optimization.

If the BSP's APIC ID in local APIC is unexpected,
a kernel panic will occur and the system will halt.
That means no need to enable APIC mode, and no reason
to set up the default routing for APIC.

The combination of default_setup_apic_routing() and
apic_bsp_setup() are used to enable APIC mode.
They two should be kept together, rather than being
separated by the codes of checking APIC ID.
Just like their usage in APIC_init_uniprocessor().

Signed-off-by: Wei Jiangang <weijg.fnst@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bp@xxxxxxx
Link: http://lkml.kernel.org/r/1471576957-12961-1-git-send-email-weijg.fnst@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/smpboot.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 2a6e84a..8216b99 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1316,14 +1316,13 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 		break;
 	}
 
-	default_setup_apic_routing();
-
 	if (read_apic_id() != boot_cpu_physical_apicid) {
 		panic("Boot APIC ID in local APIC unexpected (%d vs %d)",
 		     read_apic_id(), boot_cpu_physical_apicid);
 		/* Or can we switch back to PIC here? */
 	}
 
+	default_setup_apic_routing();
 	cpu0_logical_apicid = apic_bsp_setup(false);
 
 	pr_info("CPU%d: ", 0);