Smith scored the first of the Tigers' two tries as they dispatched tournament top seeds Leinster in emphatic fashion to book a 'home' semi-final date with Toulouse.
The French giants are also chasing a third European Cup title and are rated by Johnson as probably the strongest team in the competition.
But Smith said: "Home advantage always helps. That was one of the bonuses of going out to Dublin and winning.
"It has been said French teams don't travel so well but that has changed in recent years, as Biarritz showed, and Toulouse are a fantastic side.
"But we know we have got it in us. We are a fantastic side and have a lot of confidence.
"Last week's defeat to Leeds in the Premiership was a bit of a kick up the backside but in some ways it shows how the importance of the match affects your team performance."
Dewi Morris, for one, believes "no-one will be surprised" if Smith is among the 44 players named by Sir Clive Woodward on April 11 for the trip to New Zealand.
Former England international Morris told skysports.com: "Smith has everything the Lions need as he showed with his first-half score (against Leinster).
"He has the talent, he creates space, has pace and has vision. He has everything you need for a Test centre - and as a young guy has a tremendous future."