Engine revving by it self and white smoke

I was driving on a highway and suddley the engin started revving very high and it would not stop, white smoke started to appear everywhere while the engin was just revving . I pulled to the side and switch the key and even took the car key out , but still the engin was revving at the high speed. I clicked on my key remote and then car stpped. letf it for while but the car didnt start.
I have SAAB 9-3 Diesel 2007 covertable
I then had to tow the car back
Some one told me its a turbo thats gone and it may have damage the engin as well and I may have to change the engin but not sure.
I have cehcked online and it happened to others but doesnt really say what to check and what is the reason it happens. I wonder if anyoine had the same issue ad how it was fixed