From 725dfa851f8e1de8653f41a4bd38c7f98757eb40 Mon Sep 17 00:00:00 2001
From: Igor Mammedov <imammedo@redhat.com>
Date: Mon, 2 Sep 2019 08:02:22 -0400
Subject: [PATCH] x86: do not advertise die-id in query-hotpluggbale-cpus if
 '-smp dies' is not set

Commit 176d2cda0 (i386/cpu: Consolidate die-id validity in smp context) added
new 'die-id' topology property to CPUs and exposed it via QMP command
query-hotpluggable-cpus, which broke -device/device_add cpu-foo for existing
users that do not support die-id/dies yet. That's would be fine if it happened
to new machine type only but it also happened to old machine types,
which breaks migration from old QEMU to the new one, for example following CLI:

  OLD-QEMU -M pc-i440fx-4.0 -smp 1,max_cpus=2 \
           -device qemu64-x86_64-cpu,socket-id=1,core-id=0,thread-id
is not able to start with new QEMU, complaining about invalid die-id.

After discovering regression, the patch
   "pc: Don't make die-id mandatory unless necessary"
makes die-id optional so old CLI would work.

However it's not enough as new QEMU still exposes die-id via query-hotpluggbale-cpus
QMP command, so the users that started old machine type on new QEMU, using all
properties (including die-id) received from QMP command (as required), won't be
able to start old QEMU using the same properties since it doesn't support die-id.

Fix it by hiding die-id in query-hotpluggbale-cpus for all machine types in case
'-smp dies' is not provided on CLI or -smp dies = 1', in which case smp_dies == 1
and APIC ID is calculated in default way (as it was before DIE support) so we won't
need compat code as in both cases the topology provided to guest via CPUID is the same.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20190902120222.6179-1-imammedo@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
(cherry picked from commit c6c1bb89fb46f3b88f832e654cf5a6f7941aac51)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 hw/i386/pc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 947f81070f..d011733ff7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -2887,8 +2887,10 @@ static const CPUArchIdList *pc_possible_cpu_arch_ids(MachineState *ms)
                                  ms->smp.threads, &topo);
         ms->possible_cpus->cpus[i].props.has_socket_id = true;
         ms->possible_cpus->cpus[i].props.socket_id = topo.pkg_id;
-        ms->possible_cpus->cpus[i].props.has_die_id = true;
-        ms->possible_cpus->cpus[i].props.die_id = topo.die_id;
+        if (pcms->smp_dies > 1) {
+            ms->possible_cpus->cpus[i].props.has_die_id = true;
+            ms->possible_cpus->cpus[i].props.die_id = topo.die_id;
+        }
         ms->possible_cpus->cpus[i].props.has_core_id = true;
         ms->possible_cpus->cpus[i].props.core_id = topo.core_id;
         ms->possible_cpus->cpus[i].props.has_thread_id = true;
--
2.23.0