I have an S2 visa issued in 2017 can I use it again?

I have an S2 issued in 2017 it runs out in 2019 next to entries it says M, duration of each stay is 90 days. I went to China in 2017 and stayed for two weeks and I am going again in May this year for 2 weeks. Do I have to get another entry permit or can I use this one again? Can I use it multiple times before it runs out in 2019 is my question.