In a resealable plastic bag, mix together 2 tablespoons olive oil, the mustard, maple syrup, chopped rosemary and garlic. Add the pork and turn in the mixture to coat; refrigerate for at least 1 hour or overnight.
Preheat the oven to 375 degrees . Place the rosemary sprigs in the center of a roasting pan. Arrange six 14-inch lengths of kitchen string crosswise, about 2 inches apart, in the pan. Place the marinated pork on top of the strings and rosemary. Lay the bacon slices, on an angle, over the pork loin. Tie each string around the meat to secure the bacon, then trim the loose ends.
Scatter the potatoes around the pork and drizzle with the remaining 2 tablespoons oil; toss to mix. Season the pork and potatoes with salt and pepper. Roast until an instant-read thermometer inserted into the center of the pork registers 150 degrees , about 1 hour. Let rest for 10 minutes before slicing. Serve with the potatoes.