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authorJeremy Fitzhardinge <jeremy@goop.org>2007-05-02 13:27:16 -0400
committerAndi Kleen <andi@basil.nowhere.org>2007-05-02 13:27:16 -0400
commit9ce8c2ed12550f90fd6e902990652b13df647793 (patch)
treee4fbef8305cd99c3b619220eea0fd7706da45b91 /arch/i386/kernel/head.S
parentc5413fbe894924ddb8aa474a4d4da52e7a6c7e0b (diff)
[PATCH] i386: map enough initial memory to create lowmem mappings
head.S creates the very initial pagetable for the kernel. This just maps enough space for the kernel itself, and an allocation bitmap. The amount of mapped memory is rounded up to 4Mbytes, and so this typically ends up mapping 8Mbytes of memory. When booting, pagetable_init() needs to create mappings for all lowmem, and the pagetables for these mappings are allocated from the free pages around the kernel in low memory. If the number of pagetable pages + kernel size exceeds head.S's initial mapping, it will end up faulting on an unmapped page. This will only happen with specific combinations of kernel size and memory size. This patch makes sure that head.S also maps enough space to fit the kernel pagetables as well as the kernel itself. It ends up using an additional two pages of unreclaimable memory. Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com> Signed-off-by: Andi Kleen <ak@suse.de> Acked-by: "H. Peter Anvin" <hpa@zytor.com> Cc: Andi Kleen <ak@suse.de> Cc: Zachary Amsden <zach@vmware.com> Cc: Chris Wright <chrisw@sous-sol.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Diffstat (limited to 'arch/i386/kernel/head.S')
-rw-r--r--arch/i386/kernel/head.S23
1 files changed, 19 insertions, 4 deletions
diff --git a/arch/i386/kernel/head.S b/arch/i386/kernel/head.S
index 12277d8938df..9b10af65faaa 100644
--- a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -34,17 +34,32 @@
34 34
35/* 35/*
36 * This is how much memory *in addition to the memory covered up to 36 * This is how much memory *in addition to the memory covered up to
37 * and including _end* we need mapped initially. We need one bit for 37 * and including _end* we need mapped initially.
38 * each possible page, but only in low memory, which means 38 * We need:
39 * 2^32/4096/8 = 128K worst case (4G/4G split.) 39 * - one bit for each possible page, but only in low memory, which means
40 * 2^32/4096/8 = 128K worst case (4G/4G split.)
41 * - enough space to map all low memory, which means
42 * (2^32/4096) / 1024 pages (worst case, non PAE)
43 * (2^32/4096) / 512 + 4 pages (worst case for PAE)
44 * - a few pages for allocator use before the kernel pagetable has
45 * been set up
40 * 46 *
41 * Modulo rounding, each megabyte assigned here requires a kilobyte of 47 * Modulo rounding, each megabyte assigned here requires a kilobyte of
42 * memory, which is currently unreclaimed. 48 * memory, which is currently unreclaimed.
43 * 49 *
44 * This should be a multiple of a page. 50 * This should be a multiple of a page.
45 */ 51 */
46#define INIT_MAP_BEYOND_END (128*1024) 52LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
47 53
54#if PTRS_PER_PMD > 1
55PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD
56#else
57PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
58#endif
59BOOTBITMAP_SIZE = LOW_PAGES / 8
60ALLOCATOR_SLOP = 4
61
62INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm
48 63
49/* 64/*
50 * 32-bit kernel entrypoint; only used by the boot CPU. On entry, 65 * 32-bit kernel entrypoint; only used by the boot CPU. On entry,