init_mem_mapping()
/* the ISA range is always mapped regardless of memory holes */
init_memory_mapping(0, ISA_END_ADDRESS);
...
/*
* If the allocation is in bottom-up direction, we setup direct mapping
* in bottom-up, otherwise we setup direct mapping in top-down.
*/
if (memblock_bottom_up()) {
unsigned long kernel_end = __pa_symbol(_end);
/*
* we need two separate calls here. This is because we want to
* allocate page tables above the kernel. So we first map
* [kernel_end, end) to make memory above the kernel be mapped
* as soon as possible. And then use page tables allocated above
* the kernel to map [ISA_END_ADDRESS, kernel_end).
*/
memory_map_bottom_up(kernel_end, end);
memory_map_bottom_up(ISA_END_ADDRESS, kernel_end);
} else {
memory_map_top_down(ISA_END_ADDRESS, end);
}
/*
* Set __PAGE_OFFSET to the most negative possible address +
* PGDIR_SIZE*16 (pgd slot 272). The gap is to allow a space for a
* hypervisor to fit. Choosing 16 slots here is arbitrary, but it's
* what Xen requires.
*/
#define __PAGE_OFFSET_BASE _AC(0xffff880000000000, UL)
#define __PAGE_OFFSET __PAGE_OFFSET_BASE
