Function permanent_kmaps_init() take a struct pgd_t as parameter.
I presume passing the struct pgd_t as a parameter is to make the
function flexible in order to reuse it under different cases. However,
I discover the following things imparing the rationality of this
parameter.
1. This function is invoke from one place only. That is, in
pagetable_init(), where swapper_pg_dir is passed as the parameter.
2. The function accesses swapper_pg_dir directly.
So I think either the parameter is redundent or the direct hardcoded
access to swapper_pg_dir within the function should be replaced by the
access to the parameter.