x86: fix early panic with boot option "nosmp"

Impact: fix boot crash with numcpus=0 on certain systems

Fix early exception in __get_smp_config with nosmp.

Bail out early when there is no MP table.

Reported-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Tested-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/kernel/mpparse.c b/arch/x86/kernel/mpparse.c
index f98f4e1dba09..0f4c1fd5a1f4 100644
--- a/arch/x86/kernel/mpparse.c
+++ b/arch/x86/kernel/mpparse.c
@@ -604,6 +604,9 @@ static void __init __get_smp_config(unsigned int early)
                 printk(KERN_INFO "Using ACPI for processor (LAPIC) "
                        "configuration information\n");
 
+        if (!mpf)
+                return;
+
         printk(KERN_INFO "Intel MultiProcessor Specification v1.%d\n",
                mpf->mpf_specification);
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_32)