lkl: initialize mm constants before mem_init()

max_mapnr is accessed through the following call chain:

	mem_init()
	-> memblock_free_all()
	   -> free_low_memory_core_early()
	      -> memmap_init_reserved_pages()
	         -> reserve_bootmem_region()
	            -> pfn_valid()
	               -> (pfn - ARCH_PFN_OFFSET) < max_mapnr

In lkl, max_mapnr is currently initialized in mem_init(), but only after
memblock_free_all() runs. This means pfn_valid() can see an
uninitialized max_mapnr and incorrectly return false for pfns that
should be valid.

For example, reserve_bootmem_region() should mark such pages as
reserved, but due to this bug it does not.

Other architectures, such as riscv, x86, and arm64, initialize mm
constants before mem_init() from setup_arch(). Do the equivalent for lkl
by initializing max_pfn, max_low_pfn, min_low_pfn, and max_mapnr in
bootmem_init().

Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>

Author: lrh2000

arch/lkl/mm/bootmem.c

@@ -46,10 +46,12 @@ void __init bootmem_init(unsigned long mem_sz)
 	 * Give all the memory to the bootmap allocator, tell it to put the
 	 * boot mem_map at the start of memory.
 	 */
-	max_low_pfn = virt_to_pfn((void *)memory_end);
-	min_low_pfn = virt_to_pfn((void *)memory_start);
 	memblock_add(__pa(memory_start), mem_size);
 
+	max_pfn = max_low_pfn = virt_to_pfn((void *)memory_end);
+	min_low_pfn = virt_to_pfn((void *)memory_start);
+	set_max_mapnr(max_pfn - ARCH_PFN_OFFSET);
+
 	empty_zero_page = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
 	memset(empty_zero_page, 0, PAGE_SIZE);
 
@@ -60,9 +62,6 @@ void __init bootmem_init(unsigned long mem_sz)
 void __init mem_init(void)
 {
 	memblock_free_all();
-	max_mapnr = totalram_pages();
-	max_low_pfn = max_mapnr + ARCH_PFN_OFFSET;
-	max_pfn = max_mapnr + ARCH_PFN_OFFSET;
 }
 
 /*