[PATCH] i386/x86-64: Use new official CPUID to get APICID/core split on AMD platforms

Previously the apicid<->coreid split was computed based on the max
number of cores. Now use a new CPUID AMD defined for that. On most
systems right now it should be 0 and the old method will be used.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/arch/i386/kernel/cpu/amd.c b/arch/i386/kernel/cpu/amd.c
index 786d1a57048b..b9c93d9789e7 100644
--- a/arch/i386/kernel/cpu/amd.c
+++ b/arch/i386/kernel/cpu/amd.c
@@ -224,15 +224,17 @@ static void __init init_amd(struct cpuinfo_x86 *c)
 
 #ifdef CONFIG_X86_HT
         /*
-         * On a AMD dual core setup the lower bits of the APIC id
-         * distingush the cores.  Assumes number of cores is a power
-         * of two.
+         * On a AMD multi core setup the lower bits of the APIC id
+         * distingush the cores.
          */
         if (c->x86_max_cores > 1) {
                 int cpu = smp_processor_id();
-                unsigned bits = 0;
-                while ((1 << bits) < c->x86_max_cores)
-                        bits++;
+                unsigned bits = (cpuid_ecx(0x80000008) >> 12) & 0xf;
+
+                if (bits == 0) {
+                        while ((1 << bits) < c->x86_max_cores)
+                                bits++;
+                }
                 cpu_core_id[cpu] = phys_proc_id[cpu] & ((1<<bits)-1);
                 phys_proc_id[cpu] >>= bits;
                 printk(KERN_INFO "CPU %d(%d) -> Core %d\n",