x86: introduce max_low_pfn_mapped for 64-bit

when more than 4g memory is installed, don't map the big hole below 4g.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/asm-x86/page.h b/include/asm-x86/page.h
index b52ed85f32f5..28d7b4533b1a 100644
--- a/include/asm-x86/page.h
+++ b/include/asm-x86/page.h
@@ -61,6 +61,7 @@ extern void map_devmem(unsigned long pfn, unsigned long size,
 extern void unmap_devmem(unsigned long pfn, unsigned long size,
                          pgprot_t vma_prot);
 
+extern unsigned long max_low_pfn_mapped;
 extern unsigned long max_pfn_mapped;
 
 struct page;