Peel, crush and finely mince the garlic on a cutting board.
Sprinkle the garlic with the salt and then use the back of the knife and a lot of pressure to start to rub the garlic into a paste. The salt will allow you to break the garlic down into a paste as you rub it with the back of the knife. Repeat the process until you get a nice paste consistency.
Remove and then mince the leaves of 4 of the the rosemary sprigs, saving the stems and remaining sprigs until later in the recipe.
Combine the garlic, rosemary, olive oil and a few turns of black pepper in a small bowl and mix thoroughly to form a paste.
Pat the pork tenderloin dry with a paper towel and then rub with the garlic and rosemary paste.
Allow the pork to sit at room temperature for about 20 minutes to marinate.
Light the grill and prepare for medium direct grilling.
Once the grill is ready and the pork tenderloin has marinated for 20 minutes, throw the 2 remaining rosemary sprigs and reserved sprigs down into the fire and then immediately place the pork tenderloin over the now smoldering rosemary and then close the lid of the grill.
Grill for about 6 minutes and then open the lid of the grill and turn the pork tenderloin 1/4 turn. Treat the pork tenderloin like it has 4 sides, we are going to grill all 4 sides to get it nice and even.
Continue to grill the pork 6 minutes per side until it reaches an internal temperature of around 145 degrees.
Remove the pork tenderloin from the grill, cover with aluminum foil and let rest for 8 minutes before slicing.