Probably just old hardened valve stem seals. They let some oil into the cylinders, especially on the left side when you park on the side stand overnight.
If the smoke clears after a couple of miles, it isn't a big worry.
I went for a couple of years with a small amount of white smoke out the right side at
startup. About a month ago I started after a fillup at a gas station and I had clouds of
white smoke billowing out the right side. Pulled away from the pumps before the
attendant panicked and let it run for a minute or two. Cleared up back to normal but
the temp gauge ran up to just below the red and stayed there while driving. Two days
later the engine wouldn't turn over. Pulled the number three plug, turned the engine
over, and shot anti-freeze all over the garage wall! I'm in the process of replacing the
head gasket on the right side and the timing belts.
I suggest pulling the plugs and comparing colours. And have you had to add anti-freeze lately?
And if you're continuing to ride as-is then take the spark plug wrench with you.
+1 on Dennis's comment. Condensation will form inside both pipes equally and vaporize as the pipes warm up. White smoke from one side is likely signs of a head gasket failing. If you have to do a head gasket job use OEM head gaskets. It's not a job you want to practice over and over.
My '83 has smoked on start-up from the left side for years. I freaked when it happened the first time, read on this forum that was somewhat normal. The bike runs very well to this day. It doesn't take much oil to produce the smoke and mine might smoke for a minute or so.
That being said, what's it smell like? If it's a sweet smell, it's anti-freeze. If it smells like oil, fuggeabotit. If you're not fouling plugs on the left side and you're not using a lot oil, get on it and ride it.Put it on the centerstand and see if the problem goes away. Also, make sure you haven't over-filled the oil level.
Try this, when you come in from a ride after killing engine ,lean bike to the right for a minute. This will allow excess oil in cylinder to drain,then put on side stand.Be sure to turn fuel petcock off.