template.html

{% if not is_viewing_all %}<a href="your_url_here">View All</a>{% endif %}

views.py

class MyView(generic.DetailView):   # Whatever View you're working with.
    def is_viewing_all(self):
        return 'view_all' in self.request.GET

    def get_context_data(self, **kwargs):
        ctx = super(MyView, self).get_context_data(**kwargs)

        # This is the important line, the rest is assumed to just use
        # whatever is already within your current get_context_data.
        ctx['is_viewing_all'] = self.is_viewing_all()

        return ctx