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@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@suse.de
Link: http://lkml.kernel.org/r/1471576957-12961-1-git-send-email-weijg.fnst@cn.fujitsu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 2a6e84a30a546f022331c653ec0725bd73086bc5..8216b997c1c91b0dfaff7095567130111e8b5bde 100644 (file)
--- 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);