Absolute value circuit around a non-zero value
In general you can just take an absolute value circuit and substitute a 10V reference for whatever it uses for a zero reference (which may be a power supply or something else). You will have to take care that there is enough power supply headroom, of course.  

Here is a modification of a standard circuit:



to do what you want with, an LTspice simulation: 



The blue trace is the input, the green is the output. Where the output goes flat at the beginning and end, it is saturating near the positive rail (+20V in this case). 

This particular circuit does need a negative supply, however the +10V reference input is high impedance so you may be able to use a voltage divider etc.