I haven't seen this as close up as your photo, but...for the last 3 seasons I've had what looks like salt or sugar on my leaves with these small oval things that look like scale. I did a search for 'tomato scale' and found....Potato/tomato psyllid. The description that was given was exactly what I had, and sure seems like what you had. Try to 'google' Potato/tomato psyllid and see what you get. I'm sorry you have this, but glad I'm not the only one. I'm don't know what your gardening practices are but if you don't spray and the infestation is early, you could probably just wipe them off with your fingers. That's what I've been doing. (Unless of course you have lots of plants)
Good luck

Suze 9 posted this great link in answer to a similar question-talks about controls, etc.

Here is a link that might be useful: Psyllids

Oh no....I have about three tree mallows about 20 feet away in my neighbors yard. No wonder I've had these little creatures every year. My neighbors yard is 'host city'.