[PATCH 1/2] hw/386: Fix uninitialized memory with -device and CPU hotplug

[Babu Moger]

Noticed the following command failure while testing CPU hotplug.

$ qemu-system-x86_64 -machine q35,accel=kvm -smp 1,maxcpus=2,
  cores=1, threads=1,sockets=2 -cpu EPYC -device EPYC-x86_64-
  cpu,core-id=0,socket-id=1,thread-id=0

  qemu-system-x86_64: -device EPYC-x86_64-cpu,core-id=0,socket-id=1,
  thread-id=0: Invalid CPU [socket: 21855, die: 0, core: 0, thread: 0]
  with APIC ID 21855, valid index range 0:1

This happens because APIC ID is calculated using uninitialized memory.
This is happening after the addition of new field node_id in X86CPUTopoIDs
structure. The node_id field is uninitialized while calling
apicid_from_topo_ids. The problem is discussed in the thread below.
20200602171838.GG577771@habkost.net/">https://lore.kernel.org/qemu-devel/20200602171838.GG577771@habkost.net/

Fix the problem by initializing the node_id properly.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
 hw/i386/pc.c               |    2 ++
 include/hw/i386/topology.h |   11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 2128f3d6fe..974cc30891 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1585,6 +1585,8 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
         topo_ids.die_id = cpu->die_id;
         topo_ids.core_id = cpu->core_id;
         topo_ids.smt_id = cpu->thread_id;
+        topo_ids.node_id = cpu_x86_use_epyc_apic_id_encoding(ms->cpu_type) ?
+                           x86_node_id_for_epyc(&topo_info, &topo_ids) : 0;
         cpu->apic_id = x86ms->apicid_from_topo_ids(&topo_info, &topo_ids);
     }
 
diff --git a/include/hw/i386/topology.h b/include/hw/i386/topology.h
index 07239f95f4..ee4deb84c4 100644
--- a/include/hw/i386/topology.h
+++ b/include/hw/i386/topology.h
@@ -140,6 +140,17 @@ static inline unsigned 
apicid_pkg_offset_epyc(X86CPUTopoInfo *topo_info)
            apicid_node_width_epyc(topo_info);
 }
 
+static inline unsigned x86_node_id_for_epyc(X86CPUTopoInfo *topo_info,
+                                            const X86CPUTopoIDs *topo_ids)
+{
+    unsigned nr_nodes = MAX(topo_info->nodes_per_pkg, 1);
+    unsigned cores_per_node = DIV_ROUND_UP((topo_info->dies_per_pkg *
+                                            topo_info->cores_per_die *
+                                            topo_info->threads_per_core),
+                                            nr_nodes);
+
+    return (topo_ids->core_id / cores_per_node) % nr_nodes;
+}
 /*
  * Make APIC ID for the CPU based on Pkg_ID, Core_ID, SMT_ID
  *