void memory_region_del_subregion(MemoryRegion *mr,
                                 MemoryRegion *subregion)
{
    memory_region_transaction_begin();
    assert(subregion->container == mr);
    subregion->container = NULL;
    QTAILQ_REMOVE(&mr->subregions, subregion, subregions_link);
    mr->uc->memory_region_update_pending = true;
    memory_region_transaction_commit(mr);
}