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Commit 2bd2753f authored by Yinghai Lu's avatar Yinghai Lu Committed by H. Peter Anvin
Browse files

x86: put initial_pg_tables into .bss 



Impact: makes vmlinux section information more useful

Don't use ram after _end blindly for pagetables. aka init pages is before _end
put those pg table into .bss

[Adapted to use brk segment - Jeremy]

v2: keep initial page table up to 512M only.
v4: put initial page tables just before _end

Signed-off-by: default avatarYinghai Lu <yinghai@kernel.org>
Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 796216a5

arch/x86/kernel/head_32.S

+14 −29
Original line number Diff line number Diff line
@@ -41,41 +41,28 @@ 
 * This is how much memory *in addition to the memory covered up to

 * and including _end* we need mapped initially.

 * We need:

 *  - one bit for each possible page, but only in low memory, which means

 *     2^32/4096/8 = 128K worst case (4G/4G split.)

 *  - enough space to map all low memory, which means

 *     (2^32/4096) / 1024 pages (worst case, non PAE)

 *     (2^32/4096) / 512 + 4 pages (worst case for PAE)

 *  - a few pages for allocator use before the kernel pagetable has

 *     been set up

 *     (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)

 *     (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)

 *

 * Modulo rounding, each megabyte assigned here requires a kilobyte of

 * memory, which is currently unreclaimed.

 *

 * This should be a multiple of a page.

 *

 * KERNEL_IMAGE_SIZE should be greater than pa(_end)

 * and small than max_low_pfn, otherwise will waste some page table entries

 */

LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT



/*

 * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate

 * pagetables from above the 16MB DMA limit, so we'll have to set

 * up pagetables 16MB more (worst-case):

 */

#ifdef CONFIG_DEBUG_PAGEALLOC

LOW_PAGES = LOW_PAGES + 0x1000000

#endif



#if PTRS_PER_PMD > 1

PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD

#else

PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)

#endif

BOOTBITMAP_SIZE = LOW_PAGES / 8

ALLOCATOR_SLOP = 4



INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm



RESERVE_BRK(pagetables, PAGE_TABLE_SIZE * PAGE_SIZE)

INIT_MAP_SIZE = (PAGE_TABLE_SIZE + ALLOCATOR_SLOP) * PAGE_SIZE_asm

RESERVE_BRK(pagetables, INIT_MAP_SIZE)



/*

 * 32-bit kernel entrypoint; only used by the boot CPU.  On entry,
@@ -168,10 +155,10 @@ num_subarch_entries = (. - subarch_entries) / 4 


/*

 * Initialize page tables.  This creates a PDE and a set of page

 * tables, which are located immediately beyond _end.  The variable

 * tables, which are located immediately beyond __brk_base.  The variable

 * _brk_end is set up to point to the first "safe" location.

 * Mappings are created both at virtual address 0 (identity mapping)

 * and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.

 * and PAGE_OFFSET for up to _end.

 *

 * Note that the stack is not yet set up!

 */
@@ -210,10 +197,9 @@ default_entry: 
	loop 11b



	/*

	 * End condition: we must map up to and including INIT_MAP_BEYOND_END

	 * bytes beyond the end of our own page tables.

	 * End condition: we must map up to the end.

	 */

	leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp

	movl $pa(_end) + PTE_IDENT_ATTR, %ebp

	cmpl %ebp,%eax

	jb 10b

1:
@@ -243,11 +229,9 @@ page_pde_offset = (__PAGE_OFFSET >> 20); 
	addl $0x1000,%eax

	loop 11b

	/*

	 * End condition: we must map up to and including INIT_MAP_BEYOND_END

	 * bytes beyond the end of our own page tables; the +0x007 is

	 * the attribute bits

	 * End condition: we must map up to end

	 */

	leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp

	movl $pa(_end) + PTE_IDENT_ATTR, %ebp

	cmpl %ebp,%eax

	jb 10b

	addl $__PAGE_OFFSET, %edi
@@ -638,6 +622,7 @@ swapper_pg_fixmap: 
	.fill 1024,4,0

ENTRY(empty_zero_page)

	.fill 4096,1,0



/*

 * This starts the data section.

 */

arch/x86/kernel/vmlinux_32.lds.S

+6 −0
Original line number Diff line number Diff line
@@ -210,6 +210,12 @@ SECTIONS 
  DWARF_DEBUG

}



/*

 * Build-time check on the image size:

 */

ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),

	"kernel image bigger than KERNEL_IMAGE_SIZE")



#ifdef CONFIG_KEXEC

/* Link time checks */

#include <asm/kexec.h>