SoftBank Group 9984.T lost 5.1% on concerns about falling values of its investment in tech firms, in particular Alibaba BABA.K, which has fallen over 50% from a record peak hit almost a year ago. TOKYO, Oct 5 (Reuters) - Japanese shares tumbled to one-month lows on Tuesday as spikes in oil prices stoked further worries about inflation and monetary tightening globally. "There's a sense that the assumption investors have had, that inflation will be temporary and earnings will continue to recover, may be crumbling," said Masayuki Doshida, senior market analyst at Rakuten Securities.