Page Tables Initialization

paging_init()

The page tables and paging infrastructure are initialized as follows:

• paging_init() is called by setup_arch() after the meminfo structure has been initialized and the bootmem allocator is ready. It calls the following routines:
  • memblock_set_current_limit()
  • build_mem_type_table() - builds a table of memory types. This has the page protection flags that are available for different memory types, for the current ARM processor. Different ARM processors have changed what flags they use, and where they are located in the page table entries, over the years. the 'mem_types' table encapsulates the settings for the running processor.
  • prepare_page_table() - this zeros out certain areas of the first-level page table (called pmd in this routine). For example, it zeros out the areas of the page table that will be covered by user-space (areas below the start of the kernel address space).
  • map_lowmem() - create the memory mappings (page table entries) for the lower portions of kernel memory. This is the "normal" memory that will be used by the kernel for static code and data, stack, and regular dynamic allocations.
  • devicemaps_init() - create the memory mappings for special CPU areas (e.g. cache flushing regions, and interrupt vectors) and reserved IO areas in the memory map.
  • kmap_init() - create the memory mapping for highmen ('pkmap')