[PATCH] xen: handle highmem pages correctly when shrinking a domain

[Ian Campbell <ian.campbell@citrix.com>]

This commit causes a crash if the page being released is a highmem
page.

  commit 1058a75f07b9bb8323fb5197be5526220f8b75cf
  Author: Dan Magenheimer <dan.magenheimer@oracle.com>
  Date:   Thu Jan 22 14:36:08 2009 -0800

    xen: actually release memory when shrinking domain

If a page is highmem then there is no need to unmap it.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: dan.magenheimer@oracle.com <dan.magenheimer@oracle.com>
Cc: Xen-devel <xen-devel@lists.xensource.com>
Cc: Stable Kernel <stable@kernel.org>
---
 drivers/xen/balloon.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff -r 7f26a03c3e02 -r 70c0102ea4c1 drivers/xen/balloon.c
--- a/drivers/xen/balloon.c	Fri Jan 23 14:14:59 2009 +0000
+++ b/drivers/xen/balloon.c	Fri Jan 23 16:24:09 2009 +0000
@@ -292,10 +292,13 @@
 
 		scrub_page(page);
 
-		ret = HYPERVISOR_update_va_mapping(
-			(unsigned long)__va(pfn << PAGE_SHIFT),
-			__pte_ma(0), 0);
-		BUG_ON(ret);
+		if (!PageHighMem(page)) {
+			ret = HYPERVISOR_update_va_mapping(
+				(unsigned long)__va(pfn << PAGE_SHIFT),
+				__pte_ma(0), 0);
+			BUG_ON(ret);
+                }
+
 	}
 
 	/* Ensure that ballooned highmem pages don't have kmaps. */