[PATCH UPDATED] x86: set PAE PHYSICAL_MASK_SHIFT to 44 bits.

Jeremy Fitzhardinge
2008-06-06T09:22:28Z

When a 64-bit x86 processor runs in 32-bit PAE mode, a pte can
potentially have the same number of physical address bits as the
64-bit host ("Enhanced Legacy PAE Paging"). This means, in theory,
we could have up to 52 bits of physical address in a pte.

The 32-bit kernel uses a 32-bit unsigned long to represent a pfn.
This means that it can only represent physical addresses up to 32+12=44
bits wide. Rather than widening pfns everywhere, just set 2^44 as the
Linux x86_32-PAE architectural limit for physical address size.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Jan Beulich <jbeulich@novell.com>
---
include/asm-x86/page_32.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

===================================================================
--- a/include/asm-x86/page_32.h
+++ b/include/asm-x86/page_32.h
@@ -22,7 +22,8 @@

#ifdef CONFIG_X86_PAE
-#define __PHYSICAL_MASK_SHIFT 36
+/* 44=32+12, the limit we can fit into an unsigned long pfn */
+#define __PHYSICAL_MASK_SHIFT 44
#define __VIRTUAL_MASK_SHIFT 32
#define PAGETABLE_LEVELS 3