x86-32: compute initial mapping size more accurately

Impact: simplification

We only need to map the kernel in head_32.S, not the whole of
lowmem.  We use 512MB as a reasonable (but arbitrary) limit on
the maximum size of the kernel image.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

2 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
index f1e4a79a6e4..0f915ae649a 100644
--- a/arch/x86/include/asm/page_32_types.h
+++ b/arch/x86/include/asm/page_32_types.h
@@ -39,6 +39,11 @@
 #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__
 
 /*
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index db6652710e9..3ce5456dfbe 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -54,7 +54,7 @@
  *
  * This should be a multiple of a page.
  */
-LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
+LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
 
 /*
  * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate