My minimization problem has objective function in x^TQx form, where x is unknown and Q is given positive definite matrix. It is quadratic, and is not in linear matrix form. But surprisingly cvx toolbox is giving a solution. how can it be possible?

The optimization problem is as follows:

Minimize x^TQx

subject to f(x)<=0

where Q=Q^T>0 is given and f(x) is in LMI form.