Do you CB against them? Fold preflop?

PokerStars No-Limit Hold'em, $0.10 BB (7 handed) from (Format: FlopTurnRiver)

MP1 ($4.10)
MP2 ($3.15)
CO ($7.15)
Button ($11.05)
Hero ($12.45)
BB ($2.45)
UTG ($3.60)

Preflop: Hero is SB with J, J.
1 fold, MP1 raises to $0.4, 3 folds, Hero raises to $1.2, 1 fold, MP1 calls $0.80.

Flop: ($2.50) 8, 6, K (2 players)
Hero bets $2.9, MP1 calls $2.90 (All-In).

Turn: ($8.30) 5 (2 players, 1 all-in)

River: ($8.30) 2 (2 players, 1 all-in)

Final Pot: $8.30

Preflop: Hero is SB with J, J.
1 fold, MP1 raises to $0.4, 3 folds, Hero raises to $1.2, 1 fold, MP1 calls $0.80

I don't like escalating OOP pre-flop

This is esp vs a short stack as I will have trouble getting away from stuff like 2nd pair..

I would either flat call and see if the flop is a good one (cheap to get away from if an ace falls for example) or negate my positional disadvantage with a pre-flop push.

He is 40% stacked which is not super short - that said at these stakes with the 4th best hand in poker, I would push it..