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 exercize 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>
---
 hw/core/machine.c        | 22 ++++++++++++++++++++++
 include/hw/core/boards.h |  6 ++++++
 system/runstate.c        | 17 +++++++++--------
 3 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 6411e68856..95d7650db9 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -450,6 +450,21 @@ 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);
@@ -1198,6 +1213,13 @@ 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",
+        "Generate new accelerator fd on reset, "
+        "to be used only for testing and 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",
diff --git a/include/hw/core/boards.h b/include/hw/core/boards.h
index 07f8938752..ee3cc9130e 100644
--- a/include/hw/core/boards.h
+++ b/include/hw/core/boards.h
@@ -447,6 +447,12 @@ struct MachineState {
     struct NVDIMMState *nvdimms_state;
     struct NumaState *numa_state;
     bool acpi_spcr_enabled;
+    /*
+     * whether to change virtual machine accelerator file descriptor upon
+     * reset or not. used only for debugging and testing purpose.
+     * It should be set to false for all regular use.
+     */
+    bool new_accel_vmfd_on_reset;
 };
 
 /*
diff --git a/system/runstate.c b/system/runstate.c
index d2ece27729..06036a9170 100644
--- a/system/runstate.c
+++ b/system/runstate.c
@@ -525,22 +525,23 @@ void qemu_system_reset(ShutdownCause reason)
         type = RESET_TYPE_COLD;
     }
 
-    /*
-     * different accelerators implement how to close the old file handle of
-     * the accelerator descriptor and create a new one here. Resetting
-     * file handle is necessary to create a new confidential VM context post
-     * VM reset.
-     */
-    if (!cpus_are_resettable() && reason == SHUTDOWN_CAUSE_GUEST_RESET) {
+    if (reason == SHUTDOWN_CAUSE_GUEST_RESET &&
+        (current_machine->new_accel_vmfd_on_reset || !cpus_are_resettable())) {
         if (ac->reset_vmfd) {
             ret = ac->reset_vmfd(current_machine);
             if (ret < 0) {
                 error_report("unable to reset vmfd: %s(%d)",
                              strerror(-ret), ret);
                 vm_stop(RUN_STATE_INTERNAL_ERROR);
+            } else if (current_machine->new_accel_vmfd_on_reset) {
+                info_report("virtual machine accel file descriptor "
+                            "has changed.");
             }
+        } else if (!cpus_are_resettable())  {
+            error_report("accelerator does not support reset!");
         } else {
-            error_report("accelerator does not support reset");
+            error_report("accelerator does not support vmfd change reset, "
+                         "proceeding with normal reset!");
         }
     }
 
-- 
2.42.0