I would not assume that Voldemort doesn't know about it. He watched Harry do it during the temper tantrum in the woods just before the centaur attack, and there was also the Azkaban escape. Quirrel would not have missed that such a hole should be beyond a first year's magic, and Harry straight up told him that it was something that would ID Harry. Azkaban alone would not have been enough to tell him what exactly had been done, though he might guess, but it would certainly prime him to be paying close attention when Harry started silently slicing a bunch of trees in half.

Ch. 58:

A brief and terrible magic lashed out from the Defense Professor's wand, scouring the hole in the wall, scarring the huge chunk of metal that lay in the room's midst; as Harry had requested, saying that the method he'd used might identify him.

Ch. 72:

The Severing Charm wouldn't bring down a tree, so he'd started partially Transfiguring cross-sections through the wood. It hadn't let out what was inside him, bringing down a small circle of trees hadn't made him feel any better...

"Well," the man in the black cloak said thoughtfully, "you needed to fly into a rage and have a loud tantrum in the Forbidden Forest in the middle of the night, and I needed to go just outside your ability to detect me and keep watch.