runstate: skip initial CPU reset if reset is not actually possible

Right now, the system reset is concluded by a call to
cpu_synchronize_all_post_reset() in order to sync any changes
that the machine reset callback applied to the CPU state.

However, for VMs with encrypted state such as SEV-ES guests (currently
the only case of guests with non-resettable CPUs) this cannot be done,
because guest state has already been finalized by machine-init-done notifiers.
cpu_synchronize_all_post_reset() does nothing on these guests, and actually
we would like to make it fail if called once guest has been encrypted.
So, assume that boards that support non-resettable CPUs do not touch
CPU state and that all such setup is done before, at the time of
cpu_synchronize_all_post_init().

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/system/runstate.c b/system/runstate.c
index d6ab860eca..cb4905a40f 100644
--- a/system/runstate.c
+++ b/system/runstate.c
@@ -501,7 +501,20 @@ void qemu_system_reset(ShutdownCause reason)
     default:
         qapi_event_send_reset(shutdown_caused_by_guest(reason), reason);
     }
-    cpu_synchronize_all_post_reset();
+
+    /*
+     * Some boards use the machine reset callback to point CPUs to the firmware
+     * entry point.  Assume that this is not the case for boards that support
+     * non-resettable CPUs (currently used only for confidential guests), in
+     * which case cpu_synchronize_all_post_init() is enough because
+     * it does _more_  than cpu_synchronize_all_post_reset().
+     */
+    if (cpus_are_resettable()) {
+        cpu_synchronize_all_post_reset();
+    } else {
+        assert(runstate_check(RUN_STATE_PRELAUNCH));
+    }
+
     vm_set_suspended(false);
 }