There are literally thousands of these things. I've got one right now that I can't ID, possibly Viola papilionacea. Come to think of it, I have another violet I can't ID and haven't been able to come close for about 2 years. I've got a few that are white but they aren't like yours. I have Viola sororia bi-color, V. 'Freckles', and V. canadensis so I could post photos of these for you to be able to compare. I don't think yours is Viola blanca, V. pallens, V. renifolia, or V. macloskeyi as the leaves are all wrong. You might want to check for images of Viola lanceolata. If it isn't V. lanceolata, I have absolutely no idea what it is. Supposedly, I have V. lanceolata here somewhere but I have never run across it yet. Sorry, I struggle with violets myself.