The response of the Autpilot, Autothrust and FBW Flight Control System of an Airbus A320/A330/A340 to an updraft in cruise will depend on the updraft velocity and rate-of-buildup. If the updraft is strong enough to trigger the high-angle-of-attack protection (alphaprot) of the FBW system, the autopilot disengages. In the absence of pilot control inputs on the sidestick, the FBW system will tend to maintain the angle of attack at a fixed value equal to alphaprot. The airplane will then enter a steep climb at the expense of airspeed up to a certain altitude, and will then start to descend. The speed at the apogee can be well below stall speed, but the airplane will not stall because alphaprot is less than the stall angle of attack.
There have been at least two incidents of this nature to A330/A340 airplanes, one of which is reported here:
Incident Report Airbus A340-314 F-GLZU 22 July 2011 in cruise at FL350.
Alphafloor is an autothrust function that is triggered at an angle of attack greater than alphaprot. If triggered, it will increase thrust to maximum takeoff thrust. However, since takeoff thrust at cruise altitude is not much greater than normal cruise thrust, the effect of alphafloor activation would be relatively insignificant.