[PATCH v2 3/3] 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.
https://lore.kernel.org/qemu-devel/20200602171838.GG577771@habkost.net/

Fix the problem by initializing the node_id from the device being added.

Fixes:
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1828750

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
 hw/i386/pc.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index e613b2299f..aa9fb48834 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1553,6 +1553,15 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
             cpu->die_id = 0;
         }
 
+        /*
+         * If node_id is not set, initialize it to zero for now. If the user
+         * does not pass the correct node in case of numa configuration, it
+         * will be rejected eventually.
+         */
+        if (cpu->node_id < 0) {
+            cpu->node_id = 0;
+        }
+
         if (cpu->socket_id < 0) {
             error_setg(errp, "CPU socket-id is not set");
             return;
@@ -1587,6 +1596,7 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
         }
 
         topo_ids.pkg_id = cpu->socket_id;
+        topo_ids.node_id = cpu->node_id;
         topo_ids.die_id = cpu->die_id;
         topo_ids.core_id = cpu->core_id;
         topo_ids.smt_id = cpu->thread_id;