migration: preserve suspended for snapshot

Restoring a snapshot can break a suspended guest.  Snapshots suffer from
the same suspended-state issues that affect live migration, plus they must
handle an additional problematic scenario, which is that a running vm must
remain running if it loads a suspended snapshot.

To save, the existing vm_stop call now completely stops the suspended
state.  Finish with vm_resume to leave the vm in the state it had prior
to the save, correctly restoring the suspended state.

To load, if the snapshot is not suspended, then vm_stop + vm_resume
correctly handles all states, and leaves the vm in the state it had prior
to the load.  However, if the snapshot is suspended, restoration is
trickier.  First, call vm_resume to restore the state to suspended so the
current state matches the saved state.  Then, if the pre-load state is
running, call wakeup to resume running.

Prior to these changes, the vm_stop to RUN_STATE_SAVE_VM and
RUN_STATE_RESTORE_VM did not change runstate if the current state was
suspended, but now it does, so allow these transitions.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/1704312341-66640-8-git-send-email-steven.sistare@oracle.com
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/system/vl.c b/system/vl.c
index 6b87bfa..1eec5f6 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -2710,7 +2710,9 @@ void qmp_x_exit_preconfig(Error **errp)
     qemu_machine_creation_done();
 
     if (loadvm) {
+        RunState state = autostart ? RUN_STATE_RUNNING : runstate_get();
         load_snapshot(loadvm, NULL, false, NULL, &error_fatal);
+        load_snapshot_resume(state);
     }
     if (replay_mode != REPLAY_MODE_NONE) {
         replay_vmstate_init();