hw/machine: introduce machine specific option 'x-change-vmfd-on-reset'

A new machine specific option 'x-change-vmfd-on-reset' is introduced for
debugging and testing only (hence the 'x-' prefix). This option when enabled
will force KVM VM file descriptor to be changed upon guest reset like
in the case of confidential guests. This can be used to exercise the code
changes that are specific for confidential guests on non-confidential
guests as well (except changes that require hardware support for
confidential guests).
A new functional test has been added in the next patch that uses this new
parameter to test the VM file descriptor changes.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
Link: https://lore.kernel.org/r/20260225035000.385950-33-anisinha@redhat.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/core/machine.c

@@ -435,6 +435,21 @@ static void machine_set_dump_guest_core(Object *obj, bool value, Error **errp)
     ms->dump_guest_core = value;
 }
 
+static bool machine_get_new_accel_vmfd_on_reset(Object *obj, Error **errp)
+{
+    MachineState *ms = MACHINE(obj);
+
+    return ms->new_accel_vmfd_on_reset;
+}
+
+static void machine_set_new_accel_vmfd_on_reset(Object *obj,
+                                                bool value, Error **errp)
+{
+    MachineState *ms = MACHINE(obj);
+
+    ms->new_accel_vmfd_on_reset = value;
+}
+
 static bool machine_get_mem_merge(Object *obj, Error **errp)
 {
     MachineState *ms = MACHINE(obj);
@@ -1183,6 +1198,13 @@ static void machine_class_init(ObjectClass *oc, const void *data)
     object_class_property_set_description(oc, "dump-guest-core",
         "Include guest memory in a core dump");
 
+    object_class_property_add_bool(oc, "x-change-vmfd-on-reset",
+        machine_get_new_accel_vmfd_on_reset,
+        machine_set_new_accel_vmfd_on_reset);
+    object_class_property_set_description(oc, "x-change-vmfd-on-reset",
+        "Set on/off to enable/disable generating new accelerator guest handle "
+         "on guest reset. Default: off (used only for testing/debugging).");
+
     object_class_property_add_bool(oc, "mem-merge",
         machine_get_mem_merge, machine_set_mem_merge);
     object_class_property_set_description(oc, "mem-merge",

include/hw/core/boards.h

@@ -448,6 +448,12 @@ struct MachineState {
     struct NVDIMMState *nvdimms_state;
     struct NumaState *numa_state;
     bool acpi_spcr_enabled;
+    /*
+     * Whether to change virtual machine accelerator handle upon
+     * reset or not. Used only for debugging and testing purpose.
+     * Set to false by default for all regular use.
+     */
+    bool new_accel_vmfd_on_reset;
 };
 
 /*

system/runstate.c

@@ -526,9 +526,9 @@ void qemu_system_reset(ShutdownCause reason)
         type = RESET_TYPE_COLD;
     }
 
-    if (!cpus_are_resettable() &&
-        (reason == SHUTDOWN_CAUSE_GUEST_RESET ||
-         reason == SHUTDOWN_CAUSE_HOST_QMP_SYSTEM_RESET)) {
+    if ((reason == SHUTDOWN_CAUSE_GUEST_RESET ||
+         reason == SHUTDOWN_CAUSE_HOST_QMP_SYSTEM_RESET) &&
+        (current_machine->new_accel_vmfd_on_reset || !cpus_are_resettable())) {
         if (ac->rebuild_guest) {
             ret = ac->rebuild_guest(current_machine);
             if (ret < 0) {