i386: vmalloc size fix

Booting kernel with vmalloc=[any size<=16m] will oops on my pc (i386/1G memory).

BUG_ON in arch/x86/mm/init_32.c triggered:
BUG_ON((unsigned long)high_memory > VMALLOC_START);

It's due to the vm area hole.

In include/asm-x86/pgtable_32.h:
#define VMALLOC_OFFSET	(8 * 1024 * 1024)
#define VMALLOC_START	(((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) \
			 & ~(VMALLOC_OFFSET - 1))

There's several related point:
1. MAXMEM :
 (-__PAGE_OFFSET - __VMALLOC_RESERVE).
The space after VMALLOC_END is included as well, I set it to
(VMALLOC_END - PAGE_OFFSET - __VMALLOC_RESERVE)

2. VMALLOC_OFFSET is not considered in __VMALLOC_RESERVE
fixed by adding VMALLOC_OFFSET to it.

3. VMALLOC_START :
 (((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) & ~(VMALLOC_OFFSET - 1))
So it's not always 8M, bigger than 8M possible.
I set it to ((unsigned long)high_memory + VMALLOC_OFFSET)

4. the VMALLOC_RESERVE is an unused macro, so remove it here.

Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Cc: akpm@linux-foundation.org
Cc: hidave.darkstar@gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/include/asm-x86/pgtable_32.h b/include/asm-x86/pgtable_32.h
index 5c3b26567a95..9bb5269475cc 100644
--- a/include/asm-x86/pgtable_32.h
+++ b/include/asm-x86/pgtable_32.h
@@ -56,8 +56,7 @@ void paging_init(void);
  * area for the same reason. ;)
  */
 #define VMALLOC_OFFSET  (8 * 1024 * 1024)
-#define VMALLOC_START   (((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) \
-                         & ~(VMALLOC_OFFSET - 1))
+#define VMALLOC_START   ((unsigned long)high_memory + VMALLOC_OFFSET)
 #ifdef CONFIG_X86_PAE
 #define LAST_PKMAP 512
 #else
@@ -73,6 +72,8 @@ void paging_init(void);
 # define VMALLOC_END    (FIXADDR_START - 2 * PAGE_SIZE)
 #endif
 
+#define MAXMEM  (VMALLOC_END - PAGE_OFFSET - __VMALLOC_RESERVE)
+
 /*
  * Define this if things work differently on an i386 and an i486:
  * it will (on an i486) warn about kernel memory accesses that are