Do I need a visa for China at all?

I will be visiting Shanghai March 15 - 18, 2018 and Hong Kong March 20 - 22, 2018, on a cruise ship.

I am a US citizen. I will be leaving for this trip on an extended itinerary as of Sept 10, 2017 and will not return to the US between that departure and when I would arrive in China.

Can you report with authority whether I need to obtain an entry permit for that short visit.

Time is of the essence.