[Xen-devel] [RFC, PATCH 7/24] i386 Vmi memory hole

[Zachary Amsden <zach@xxxxxxxxxx>]

Create a configurable hole in the linear address space at the top
of memory.  A more advanced interface is needed to negotiate how
much space the hypervisor is allowed to steal, but in the end, it
seems most likely that a fixed constant size will be chosen for
the compiled kernel, potentially propagated to an information
page used by paravirtual initialization to determine interface
compatibility.

Signed-off-by: Zachary Amsden <zach@xxxxxxxxxx>

Index: linux-2.6.16-rc3/arch/i386/Kconfig
===================================================================
--- linux-2.6.16-rc3.orig/arch/i386/Kconfig     2006-02-22 16:09:04.000000000 
-0800
+++ linux-2.6.16-rc3/arch/i386/Kconfig  2006-02-22 16:33:27.000000000 -0800
@@ -201,6 +201,15 @@ config VMI_DEBUG
 
 endmenu
 
+config MEMORY_HOLE
+       int "Create hole at top of memory (0-256 MB)"
+       range 0 256
+       default "64" if X86_VMI
+       default "0" if !X86_VMI
+       help
+          Useful for creating a hole in the top of memory when running
+          inside of a virtual machine monitor.
+
 config ACPI_SRAT
        bool
        default y
Index: linux-2.6.16-rc3/include/asm-i386/fixmap.h
===================================================================
--- linux-2.6.16-rc3.orig/include/asm-i386/fixmap.h     2006-02-22 
15:48:23.000000000 -0800
+++ linux-2.6.16-rc3/include/asm-i386/fixmap.h  2006-02-22 16:33:27.000000000 
-0800
@@ -20,7 +20,7 @@
  * Leave one empty page between vmalloc'ed areas and
  * the start of the fixmap.
  */
-#define __FIXADDR_TOP  0xfffff000
+#define __FIXADDR_TOP  0xfffff000-(CONFIG_MEMORY_HOLE << 20)
 
 #ifndef __ASSEMBLY__
 #include <linux/kernel.h>

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