[PULL 31/42] migration: Synchronize all CPU states only for non-iterable dump

[Fabiano Rosas]

From: Peter Xu <peterx@redhat.com>

Do one shot cpu sync at qemu_savevm_state_complete_precopy_non_iterable(),
instead of coding it separately in two places.

Note that in the context of qemu_savevm_state_complete_precopy(), this
patch is also an optimization for postcopy path, in that we can avoid sync
cpu twice during switchover: before this patch, postcopy_start() invokes
twice on qemu_savevm_state_complete_precopy(), each of them will try to
sync CPU info.  In reality, only one of them would be enough.

For background snapshot, there's no intended functional change.

Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: 20250114230746.3268797-7-peterx@redhat.com">https://lore.kernel.org/r/20250114230746.3268797-7-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/migration.c | 6 +-----
 migration/savevm.c    | 5 +++--
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index d8a6bc12e0..46e30a4814 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -3749,11 +3749,7 @@ static void *bg_migration_thread(void *opaque)
     if (migration_stop_vm(s, RUN_STATE_PAUSED)) {
         goto fail;
     }
-    /*
-     * Put vCPUs in sync with shadow context structures, then
-     * save their state to channel-buffer along with devices.
-     */
-    cpu_synchronize_all_states();
+
     if (qemu_savevm_state_complete_precopy_non_iterable(fb, false)) {
         goto fail;
     }
diff --git a/migration/savevm.c b/migration/savevm.c
index 5e56a5d9fc..92e77ca92b 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1531,6 +1531,9 @@ int 
qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
     Error *local_err = NULL;
     int ret;
 
+    /* Making sure cpu states are synchronized before saving non-iterable */
+    cpu_synchronize_all_states();
+
     QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
         if (se->vmsd && se->vmsd->early_setup) {
             /* Already saved during qemu_savevm_state_setup(). */
@@ -1584,8 +1587,6 @@ int qemu_savevm_state_complete_precopy(QEMUFile *f, bool 
iterable_only)
 
     trace_savevm_state_complete_precopy();
 
-    cpu_synchronize_all_states();
-
     if (!in_postcopy || iterable_only) {
         ret = qemu_savevm_state_complete_precopy_iterable(f, in_postcopy);
         if (ret) {
-- 
2.35.3