1 files changed, 13 insertions, 7 deletions

diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index fb850b52b4da..1cb3e21c571a 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -873,10 +873,18 @@ static void __init amd_detect_cmp(struct cpuinfo_x86 *c)
         int node = 0;
         unsigned apicid = hard_smp_processor_id();
 #endif
+        unsigned ecx = cpuid_ecx(0x80000008);
 
-        bits = 0;
-        while ((1 << bits) < c->x86_max_cores)
-                bits++;
+        c->x86_max_cores = (ecx & 0xff) + 1;
+
+        /* CPU telling us the core id bits shift? */
+        bits = (ecx >> 12) & 0xF;
+
+        /* Otherwise recompute */
+        if (bits == 0) {
+                while ((1 << bits) < c->x86_max_cores)
+                        bits++;
+        }
 
         /* Low order bits define the core id (index of core in socket) */
         cpu_core_id[cpu] = phys_proc_id[cpu] & ((1 << bits)-1);
@@ -964,11 +972,9 @@ static int __init init_amd(struct cpuinfo_x86 *c)
         if (c->x86_power & (1<<8))
                 set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
 
-        if (c->extended_cpuid_level >= 0x80000008) {
-                c->x86_max_cores = (cpuid_ecx(0x80000008) & 0xff) + 1;
-
+        /* Multi core CPU? */
+        if (c->extended_cpuid_level >= 0x80000008)
                 amd_detect_cmp(c);
-        }
 
         return r;
 }