Pat the pork dry and place it in a 5 to 7 quart slow cooker, fat side up if there is a fat cap.
Whisk the honey, mustard, and salt until smooth. Pour over the pork and turn the roast to coat all sides.
Cover and cook on Low for 7 to 9 hours or High for 3 1/2 to 4 1/2 hours, until the pork is very tender and pulls apart easily with a fork. Check a pork loin early to prevent overcooking.
Transfer the pork to a cutting board and rest for 10 minutes. Skim excess fat from the sauce. If desired, cook the sauce uncovered on High for 10 to 15 minutes to thicken it.
Slice or shred the pork. Return it to the slow cooker and toss with sauce, or serve on a platter with sauce spooned over the top.