package my::model::subclass;

. . .

sub normal_hr { # because it returns a hashref
    \%normal
}

# then:

package my::model;

. . .

sub use_subclass_package_var {
    my ($self, @cols) = @_;
    my $normal = $self->normal_hr;

    foreach my $col (@cols) {
        next unless exists $normal->{$col};

        # the rest of the code
    }
}