arch/x86/include/asm/page_32_types.h

#ifndef _ASM_X86_PAGE_32_DEFS_H
#define _ASM_X86_PAGE_32_DEFS_H

#include <linux/const.h>

/*
 * This handles the memory map.
 *
 * A __PAGE_OFFSET of 0xC0000000 means that the kernel has
 * a virtual address space of one gigabyte, which limits the
 * amount of physical memory you can use to about 950MB.
 *
 * If you want more physical memory than this then see the CONFIG_HIGHMEM4G
 * and CONFIG_HIGHMEM64G options in the kernel configuration.
 */
#define __PAGE_OFFSET_BASE	_AC(CONFIG_PAGE_OFFSET, UL)
#define __PAGE_OFFSET		__PAGE_OFFSET_BASE

#define __START_KERNEL_map	__PAGE_OFFSET

#define THREAD_SIZE_ORDER	1
#define THREAD_SIZE		(PAGE_SIZE << THREAD_SIZE_ORDER)

#define DOUBLEFAULT_STACK 1
#define NMI_STACK 0
#define DEBUG_STACK 0
#define MCE_STACK 0
#define N_EXCEPTION_STACKS 1

#ifdef CONFIG_X86_PAE
/* 44=32+12, the limit we can fit into an unsigned long pfn */
#define __PHYSICAL_MASK_SHIFT	44
#define __VIRTUAL_MASK_SHIFT	32

#else  /* !CONFIG_X86_PAE */
#define __PHYSICAL_MASK_SHIFT	32
#define __VIRTUAL_MASK_SHIFT	32
#endif	/* CONFIG_X86_PAE */

/*
 * Kernel image size is limited to 512 MB (see in arch/x86/kernel/head_32.S)
 */
#define KERNEL_IMAGE_SIZE	(512 * 1024 * 1024)

#ifndef __ASSEMBLY__

/*
 * This much address space is reserved for vmalloc() and iomap()
 * as well as fixmap mappings.
 */
extern unsigned int __VMALLOC_RESERVE;
extern int sysctl_legacy_va_layout;

extern void find_low_pfn_range(void);
extern void setup_bootmem_allocator(void);

#endif	/* !__ASSEMBLY__ */

#endif /* _ASM_X86_PAGE_32_DEFS_H */