How tall is the corridor? If it's too small the cavalier is not going to be able to mount (if it's way too small, the mount will not be able to proceed).
And it depends on the height of the corridor, if it is less then 10' high and the cavalier will be penalize in the fight if using slashing or bashing weapon (the horse itself will be about 5' high (15 hands) at the shoulder). And he might have to bend over the neck of his horse.