There were reports of guest crash on CPU hotplug, when using q35 machine
type and OVMF with SMM, due to hotplugged CPU trying to process SMI at
default SMI handler location without it being relocated by firmware first.

Fix it by refusing hotplug if firmware hasn't negotiated CPU hotplug with
SMI support while SMI broadcast is in use.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
---
v1:
   fix typos an use suggested wording in commit and error msg
   s/secure boot/smm/; s/hotplug SMI/hotplug with SMI/
      (Laszlo Ersek <lersek@redhat.com>)
---
 hw/acpi/ich9.c | 12 +++++++++++-
 hw/i386/pc.c   | 11 +++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/hw/acpi/ich9.c b/hw/acpi/ich9.c
index 6a19070cec..0acc9a3107 100644
--- a/hw/acpi/ich9.c
+++ b/hw/acpi/ich9.c
@@ -408,10 +408,20 @@ void ich9_pm_device_pre_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
     ICH9LPCState *lpc = ICH9_LPC_DEVICE(hotplug_dev);
 
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) &&
-        !lpc->pm.acpi_memory_hotplug.is_enabled)
+        !lpc->pm.acpi_memory_hotplug.is_enabled) {
         error_setg(errp,
                    "memory hotplug is not enabled: %s.memory-hotplug-support "
                    "is not set", object_get_typename(OBJECT(lpc)));
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
+        uint64_t negotiated = lpc->smi_negotiated_features;
+
+        if (negotiated & BIT_ULL(ICH9_LPC_SMI_F_BROADCAST_BIT) &&
+            !(negotiated & BIT_ULL(ICH9_LPC_SMI_F_CPU_HOTPLUG_BIT))) {
+            error_setg(errp, "cpu hotplug with SMI wasn't enabled by firmware");
+            error_append_hint(errp, "update machine type to newer than 5.1 "
+                "and firmware that suppors CPU hotplug with SMM");
+        }
+    }
 }
 
 void ich9_pm_device_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index f32e66c1b2..1d4955485b 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1500,6 +1500,17 @@ static void pc_cpu_pre_plug(HotplugHandler *hotplug_dev,
         return;
     }
 
+    if (pcms->acpi_dev) {
+        Error *local_err = NULL;
+
+        hotplug_handler_pre_plug(HOTPLUG_HANDLER(pcms->acpi_dev), dev,
+                                 &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
+
     init_topo_info(&topo_info, x86ms);
 
     env->nr_dies = x86ms->smp_dies;
-- 
2.27.0