Volatile and multithreading: is the following thread-safe?

Assume there are two threads running Thread1() and Thread2() respectively. The thread 1 just sets a global flag to tell thread 2 to quit and thread 2 periodically checks if it should quit.

volatile bool is_terminate = false;

void Thread1()
{
    is_terminate = true;
}

void Thread2()
{
    while (!is_terminate) {
        // ...
    }
}

I want to ask if the above code is safe assuming that access to is_terminate is atomic. I already know many materials state that volatile can not insure thread-safety generally. But in the situation that only one atomic variable is shared, do we really need to protect the shared variable using a lock?