From: Peter Xu <pet...@redhat.com> Implement save_postcopy_prepare(), preparing for the enablement of both multifd and postcopy.
Signed-off-by: Peter Xu <pet...@redhat.com> Signed-off-by: Prasad Pandit <p...@fedoraproject.org> --- migration/ram.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) v8: reorder patch and some typographical corrections. - https://lore.kernel.org/qemu-devel/20250318123846.1370312-1-ppan...@redhat.com/T/#t diff --git a/migration/ram.c b/migration/ram.c index 424df6d9f1..753042456e 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -4420,6 +4420,42 @@ static int ram_resume_prepare(MigrationState *s, void *opaque) return 0; } +static bool ram_save_postcopy_prepare(QEMUFile *f, void *opaque, Error **errp) +{ + int ret; + + if (migrate_multifd()) { + /* + * When multifd is enabled, source QEMU needs to make sure all the + * pages queued before postcopy starts have been flushed. + * + * The load of these pages must happen before switching to postcopy. + * It's because loading of guest pages (so far) in multifd recv + * threads is still non-atomic, so the load cannot happen with vCPUs + * running on the destination side. + * + * This flush and sync will guarantee that those pages are loaded + * _before_ postcopy starts on the destination. The rationale is, + * this happens before VM stops (and before source QEMU sends all + * the rest of the postcopy messages). So when the destination QEMU + * receives the postcopy messages, it must have received the sync + * message on the main channel (either RAM_SAVE_FLAG_MULTIFD_FLUSH, + * or RAM_SAVE_FLAG_EOS), and such message would guarantee that + * all previous guest pages queued in the multifd channels are + * completely loaded. + */ + ret = multifd_ram_flush_and_sync(f); + if (ret < 0) { + error_setg(errp, "%s: multifd flush and sync failed", __func__); + return false; + } + } + + qemu_put_be64(f, RAM_SAVE_FLAG_EOS); + + return true; +} + void postcopy_preempt_shutdown_file(MigrationState *s) { qemu_put_be64(s->postcopy_qemufile_src, RAM_SAVE_FLAG_EOS); @@ -4439,6 +4475,7 @@ static SaveVMHandlers savevm_ram_handlers = { .load_setup = ram_load_setup, .load_cleanup = ram_load_cleanup, .resume_prepare = ram_resume_prepare, + .save_postcopy_prepare = ram_save_postcopy_prepare, }; static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host, -- 2.49.0
