Calvin Harris: Don't Cry Me a River ... 'All Good' with Taylor Swift

Calvin Harris is putting on a good face ... even if he's hurting inside.

The superstar DJ stepped out Thursday in L.A. and said he's aces with Taylor Swift's new relationship with Tom Hiddleston. Check out the vid ... Calvin tries to play it cool as the ex.

On the surface he's putting on a happy face ... but as TMZ reported he's actually PISSED it went down and dirty.