[PATCH 2/3] x86/topology: Fix AMD core count

[Peter Zijlstra]

It turns out AMD gets x86_max_cores wrong when there are compute
units.

The issue is that Linux assumes:

	nr_logical_cpus = nr_cores * nr_siblings

But AMD reports its CU unit as 2 cores, but then sets num_smp_siblings
to 2 as well.

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andreas Herrmann <aherrmann@xxxxxxxx>
Reported-by: Xiong Zhou <jencce.kernel@xxxxxxxxx>
Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20160317095220.GO6344@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 arch/x86/kernel/cpu/amd.c |    8 ++++----
 arch/x86/kernel/smpboot.c |   11 ++++++-----
 2 files changed, 10 insertions(+), 9 deletions(-)

--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -313,9 +313,9 @@ static void amd_get_topology(struct cpui
 		node_id = ecx & 7;
 
 		/* get compute unit information */
-		smp_num_siblings = ((ebx >> 8) & 3) + 1;
+		cores_per_cu = smp_num_siblings = ((ebx >> 8) & 3) + 1;
+		c->x86_max_cores /= smp_num_siblings;
 		c->compute_unit_id = ebx & 0xff;
-		cores_per_cu += ((ebx >> 8) & 3);
 	} else if (cpu_has(c, X86_FEATURE_NODEID_MSR)) {
 		u64 value;
 
@@ -331,8 +331,8 @@ static void amd_get_topology(struct cpui
 		u32 cus_per_node;
 
 		set_cpu_cap(c, X86_FEATURE_AMD_DCM);
-		cores_per_node = c->x86_max_cores / nodes_per_socket;
-		cus_per_node = cores_per_node / cores_per_cu;
+		cus_per_node = c->x86_max_cores / nodes_per_socket;
+		cores_per_node = cus_per_node * cores_per_cu;
 
 		/* store NodeID, use llc_shared_map to store sibling info */
 		per_cpu(cpu_llc_id, cpu) = node_id;