[RFC 2/3] x86: cphp: prevent guest crash on CPU hotplug when broadcast SMI is in use

[Igor Mammedov]

There were reports of guest crash on CPU hotplug, when using q35 machine
type and QVMF with Secure Boot, 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 negotiatiad CPU hotplug SMI
support while SMI broadcast is in use.

Signed-off-by: Igor Mammedov <imammedo@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 2d204babc6..a22b434e0b 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 SMI was not enabled by firmware");
+            error_append_hint(errp, "update machine type to newer than 5.0 "
+                "and firmware that suppors CPU hotplug in Secure Boot mode");
+        }
+    }
 }
 
 void ich9_pm_device_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 6fe80c84d7..dc1e9157d7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1508,6 +1508,17 @@ 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;
-- 
2.26.2