From: Avihai Horon <[email protected]> Switchover ACK is checked only during precopy while the guest is still running. The last migration_can_switchover() decision and guest stop are not atomic, so a device may want to request another switchover ACK in the gap after switchover decision has been made but before the guest is stopped. Migration would then miss that request, which can increase downtime.
Cover this case by failing the migration if a switchover-ack was requested during that time. Ideally, precopy iterations should be resumed in this case, however, VFIO doesn't support going back to precopy after being stopped, so implementing such logic would require non-trivial changes to the guest start/stop flow. Given the above and that this case should be rare, failing the migration seems reasonable. Reviewed-by: Peter Xu <[email protected]> Signed-off-by: Avihai Horon <[email protected]> Link: https://lore.kernel.org/qemu-devel/[email protected] Signed-off-by: Cédric Le Goater <[email protected]> --- migration/savevm.h | 4 ++-- migration/migration.c | 4 +++- migration/savevm.c | 19 ++++++++++++++++++- 3 files changed, 23 insertions(+), 4 deletions(-) diff --git a/migration/savevm.h b/migration/savevm.h index fb92d3bc8586553c490eb03d68be3cb56c8d0554..415198423f578049c209a1e40b796cfe63b410f0 100644 --- a/migration/savevm.h +++ b/migration/savevm.h @@ -47,8 +47,8 @@ void qemu_savevm_state_complete_postcopy(QEMUFile *f); int qemu_savevm_state_complete_precopy(MigrationState *s, Error **errp); void qemu_savevm_query_pending_iter(MigrationState *s, MigPendingData *pending, bool exact); -void qemu_savevm_query_pending_final(MigrationState *s, - MigPendingData *pending); +bool qemu_savevm_query_pending_final(MigrationState *s, + MigPendingData *pending, Error **errp); int qemu_savevm_state_complete_precopy_iterable(QEMUFile *f, bool in_postcopy); bool qemu_savevm_state_postcopy_prepare(QEMUFile *f, Error **errp); void qemu_savevm_state_end(QEMUFile *f); diff --git a/migration/migration.c b/migration/migration.c index 7da86fb08aa4d694155d87b8603aeecbd31e27c0..898695a81920b7b255c7ed17b13a9065d66d8c44 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -2827,7 +2827,9 @@ static bool migration_switchover_start(MigrationState *s, Error **errp) * properly update all the dirty bitmaps to finally generate the * correct discard bitmaps; see ram_postcopy_send_discard_bitmap(). */ - qemu_savevm_query_pending_final(s, &pending); + if (!qemu_savevm_query_pending_final(s, &pending, errp)) { + return false; + } /* Inactivate disks except in COLO */ if (!migrate_colo()) { diff --git a/migration/savevm.c b/migration/savevm.c index 1f6e696c50d189370a311c25d8eb092bc41c2b24..f654a1c563df40d546e42018a3706e92fb11cfa7 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -1852,11 +1852,28 @@ void qemu_savevm_query_pending_iter(MigrationState *s, MigPendingData *pending, qemu_savevm_query_pending(s, pending, exact, false); } -void qemu_savevm_query_pending_final(MigrationState *s, MigPendingData *pending) +bool qemu_savevm_query_pending_final(MigrationState *s, MigPendingData *pending, + Error **errp) { g_assert(bql_locked()); qemu_savevm_query_pending(s, pending, true, true); + + /* + * Switchover-ack requests done after switchover decision are not allowed. + * Fail the migration in this case since we currently don't support going + * back to precopy. + */ + if (migrate_switchover_ack() && !migrate_switchover_ack_legacy() && + pending->switchover_ack_pending > 0) { + error_setg(errp, + "Switchover ACK was requested by %" PRIu32 + " devices during switchover", + pending->switchover_ack_pending); + return false; + } + + return true; } void qemu_savevm_state_cleanup(void) -- 2.54.0
