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 Cc: Borislav Petkov Cc: Thomas Gleixner Cc: Andreas Herrmann Reported-by: Xiong Zhou Fixes: 1f12e32f4cd5 ("x86/topology: Create logical package id") Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/20160317095220.GO6344@twins.programming.kicks-ass.net --- 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;