Exploring QCD phase diagram at vanishing baryon density on the lattice

I report on the current status of QCD phase diagram at vanishing baryon density. I focus on the QCD phase diagram with three degenerate quark flavor using Highly Improved Staggered Quarks on $N_{\tau}=6$ lattices. No evidence of a first order phase transition in the pion mass window of $80\lesssim m_{\pi} \lesssim 230 $MeV is found. The pion mass at the critical point where the chiral first order phase transition ends is estimated to be $m^c_{\pi} \lesssim 45$ MeV.