Those tiny yellow flowers grow in a rather arid limestone field.
Pale Madwort (Alyssum alyssoides) is an annual plant and it is one of the first to flower in this habitat. It lives in groups, sometimes there are hundreds of small plants dispersed over a few square meters.
When the flowers open you can see their four petals in the shape of a cross, typical for Brassicaceae.
You are lucky if you find it, it has become rare in Perigord.
The white flowers are not a different species, at the end of flowering the petals turn pale and stick to the developing fruit.