2 files changed, 25 insertions, 4 deletions

diff --git a/arch/i386/kernel/asm-offsets.c b/arch/i386/kernel/asm-offsets.c
index b05e85fd1c1e..27a776c9044d 100644
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -11,6 +11,7 @@
 #include <linux/suspend.h>
 #include <asm/ucontext.h>
 #include "sigframe.h"
+#include <asm/pgtable.h>
 #include <asm/fixmap.h>
 #include <asm/processor.h>
 #include <asm/thread_info.h>
@@ -96,6 +97,11 @@ void foo(void)
                  sizeof(struct tss_struct));
 
         DEFINE(PAGE_SIZE_asm, PAGE_SIZE);
+        DEFINE(PAGE_SHIFT_asm, PAGE_SHIFT);
+        DEFINE(PTRS_PER_PTE, PTRS_PER_PTE);
+        DEFINE(PTRS_PER_PMD, PTRS_PER_PMD);
+        DEFINE(PTRS_PER_PGD, PTRS_PER_PGD);
+
         DEFINE(VDSO_PRELINK_asm, VDSO_PRELINK);
 
         OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx);
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 @@
 
 /*
  * 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.)
+ * 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
  *
  * Modulo rounding, each megabyte assigned here requires a kilobyte of
  * memory, which is currently unreclaimed.
  *
  * This should be a multiple of a page.
  */
-#define INIT_MAP_BEYOND_END     (128*1024)
+LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
 
+#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
 
 /*
  * 32-bit kernel entrypoint; only used by the boot CPU.  On entry,