riding waves upwind can mean several things (to me) , but mainly side-on wind!
not so vertical going up the line not down the line.
trim upwind, cutbacks, smaller bottom turns, possibility of staying in or near barreling part of wave -maybe even IN barrel if it's big enough ...
on the other hand, if wave and wind angles not right, or weak conditions, could be slow, boring compared to downwind.
Not boring here though:
Pictures are from a related article:http://www.inmotionkitesurfing.com/2011/toeside-wave-riding-tips