iommu: Don't crash if machine is not PC_MACHINE

Currently it's possible to crash QEMU using "-device *-iommu" and
"-machine none":

  $ qemu-system-x86_64 -machine none -device amd-iommu
  qemu/hw/i386/amd_iommu.c:1140:amdvi_realize: Object 0x55627dafbc90 is not an instance of type generic-pc-machine
  Aborted (core dumped)
  $ qemu-system-x86_64 -machine none -device intel-iommu
  qemu/hw/i386/intel_iommu.c:2972:vtd_realize: Object 0x56292ec0bc90 is not an instance of type generic-pc-machine
  Aborted (core dumped)

Fix amd-iommu and intel-iommu to ensure the current machine is really a
TYPE_PC_MACHINE instance at their realize methods.

Resulting error messages:

  $ qemu-system-x86_64 -machine none -device amd-iommu
  qemu-system-x86_64: -device amd-iommu: Machine-type 'none' not supported by amd-iommu
  $ qemu-system-x86_64 -machine none -device intel-iommu
  qemu-system-x86_64: -device intel-iommu: Machine-type 'none' not supported by intel-iommu
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/i386/amd_iommu.c

@@ -21,6 +21,7 @@
  */
 #include "qemu/osdep.h"
 #include "hw/i386/amd_iommu.h"
+#include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "trace.h"
 
@@ -1137,7 +1138,19 @@ static void amdvi_realize(DeviceState *dev, Error **err)
     int ret = 0;
     AMDVIState *s = AMD_IOMMU_DEVICE(dev);
     X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(dev);
-    PCIBus *bus = PC_MACHINE(qdev_get_machine())->bus;
+    MachineState *ms = MACHINE(qdev_get_machine());
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
+    PCMachineState *pcms =
+        PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE));
+    PCIBus *bus;
+
+    if (!pcms) {
+        error_setg(err, "Machine-type '%s' not supported by amd-iommu",
+                   mc->name);
+        return;
+    }
+
+    bus = pcms->bus;
     s->iotlb = g_hash_table_new_full(amdvi_uint64_hash,
                                      amdvi_uint64_equal, g_free, g_free);
 

hw/i386/intel_iommu.c

@@ -2969,11 +2969,21 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
 
 static void vtd_realize(DeviceState *dev, Error **errp)
 {
-    PCMachineState *pcms = PC_MACHINE(qdev_get_machine());
-    PCIBus *bus = pcms->bus;
+    MachineState *ms = MACHINE(qdev_get_machine());
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
+    PCMachineState *pcms =
+        PC_MACHINE(object_dynamic_cast(OBJECT(ms), TYPE_PC_MACHINE));
+    PCIBus *bus;
     IntelIOMMUState *s = INTEL_IOMMU_DEVICE(dev);
     X86IOMMUState *x86_iommu = X86_IOMMU_DEVICE(dev);
 
+    if (!pcms) {
+        error_setg(errp, "Machine-type '%s' not supported by intel-iommu",
+                   mc->name);
+        return;
+    }
+
+    bus = pcms->bus;
     VTD_DPRINTF(GENERAL, "");
     x86_iommu->type = TYPE_INTEL;