x86: fix boot time APIC mode detection

current_cpu_data becomes valid only relatively late in the boot
process, so looking there for a particular feature early in the game
would generally give the appearance of the feature being unavailable.

Getting this wrong means that at kexec time the system would get
returned to xAPIC mode, causing disconnect_bsp_APIC() to try to access
the APIC page, which on systems with x2APIC pre-enabled will never get
set up.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 234c4dde2fd4f1182fe1a6bea6bced83fe363007
master date: 2013-05-23 13:08:32 +0200

diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index 50430d2f398c0cf1421b74cdc1b8d5ab8f8271ba..00b25f0660e99cdef6c28557e2114926f7f78232 100644 (file)
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -1473,7 +1473,7 @@ enum apic_mode current_local_apic_mode(void)
 
     /* Reading EXTD bit from the MSR is only valid if CPUID
      * says so, else reserved */
-    if ( cpu_has(&current_cpu_data, X86_FEATURE_X2APIC)
+    if ( boot_cpu_has(X86_FEATURE_X2APIC)
          && (msr_contents & MSR_IA32_APICBASE_EXTD) )
         return APIC_MODE_X2APIC;