On some architectures, the switcher can be put in the VDSO or gate-page,
which makes it unnecessary to explicitly map in the switcher.

This makes the code only do the switcher mapping if the architecture
defines LGUEST_SWITCHER_NEEDS_MAPPING in it's asm/lguest.h

Signed-off-by: Jes Sorensen <jes@sgi.com>

---
 drivers/lguest/core.c     |    9 +++++++++
 include/asm-i386/lguest.h |    2 ++
 2 files changed, 11 insertions(+)

Index: linux-2.6.23-rc3/drivers/lguest/core.c
===================================================================
--- linux-2.6.23-rc3.orig/drivers/lguest/core.c
+++ linux-2.6.23-rc3/drivers/lguest/core.c
@@ -37,7 +37,11 @@ DEFINE_MUTEX(lguest_lock);
  * Trying to map memory at a particular address is an unusual thing to do, so
  * it's not a simple one-liner.  We also set up the per-cpu parts of the
  * Switcher here.
+ *
+ * For architectures where the switcher is located in the VDSO or gate-page
+ * section, mapping in the switcher does not need to be done seperately.
  */
+#ifdef LGUEST_SWITCHER_NEEDS_MAPPING
 static __init int map_switcher(void)
 {
 	int i, err;
@@ -118,12 +122,14 @@ free_some_pages:
 out:
 	return err;
 }
+#endif
 /*:*/
 
 /* Cleaning up the mapping when the module is unloaded is almost...
  * too easy. */
 static void unmap_switcher(void)
 {
+#ifdef LGUEST_SWITCHER_NEEDS_MAPPING
 	unsigned int i;
 
 	/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
@@ -131,6 +137,7 @@ static void unmap_switcher(void)
 	/* Now we just need to free the pages we copied the switcher into */
 	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 		__free_pages(switcher_page[i], 0);
+#endif
 }
 
 /*L:305
@@ -285,6 +292,7 @@ static int __init init(void)
 		return -EPERM;
 	}
 
+#ifdef LGUEST_SWITCHER_NEEDS_MAPPING
 	/* First we put the Switcher up in very high virtual memory. */
 	err = map_switcher();
 	if (err)
@@ -296,6 +304,7 @@ static int __init init(void)
 		unmap_switcher();
 		return err;
 	}
+#endif
 
 	/* The I/O subsystem needs some things initialized. */
 	lguest_io_init();
Index: linux-2.6.23-rc3/include/asm-i386/lguest.h
===================================================================
--- linux-2.6.23-rc3.orig/include/asm-i386/lguest.h
+++ linux-2.6.23-rc3/include/asm-i386/lguest.h
@@ -9,6 +9,8 @@
 #ifndef __ASSEMBLY__
 #include <asm/desc.h>
 
+#define LGUEST_SWITCHER_NEEDS_MAPPING	1
+
 /* Every guest maps the core switcher code. */
 #define SHARED_SWITCHER_PAGES \
 	DIV_ROUND_UP(end_switcher_text - start_switcher_text, PAGE_SIZE)