Usually this kind of setup (infinity wall - common for white background) is built using drywall that can be curved between the walls and floor and the walls themselves at the corner. Chroma paint is used to cover the structure.
Re: Green screen fabric for corner setup by Steve Brame on Dec 12, 2012 at 8:42:45 pm
Here's an interesting video "how-to". If you can get past the presentation factor, which may require several views of the video, this is one of the most comprehensive and clear videos on how to accomplish the 'cove' portion of the wall corner.