Inside or out. Whitewashing is just using thinned down paint. If oil, thin with paint thinner if latex use water. Thin to the desired coverage. Can brush on and leave or wipe off.
https://www.hometalk.com/search/posts?filter=white wash stone
If your wall is outside, be sure to use exterior paint!
Here is an idea I found on Pinterest for you https://www.pinterest.com/pin/828099450213141009/