[Xen-devel] [PATCH 10/10] xfs: eagerly remove vmap mappings to avoid upsetting Xen

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

XFS leaves stray mappings around when it vmaps memory to make it
virtually contigious.  This upsets Xen if one of those pages is being
recycled into a pagetable, since it finds an extra writable mapping of
the page.

This patch solves the problem in a brute force way, by making XFS
always eagerly unmap its mappings.

[ Stable: This works around a bug in 2.6.23.  We may come up with a
better solution for mainline, but this seems like a low-impact fix for
the stable kernel. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: XFS masters <xfs-masters@xxxxxxxxxxx>
Cc: Stable kernel <stable@xxxxxxxxxx>
Cc: Morten =?utf-8?q?B=C3=B8geskov?= <xen-users@xxxxxxxxxxxxxxxxxx>
Cc: Mark Williamson <mark.williamson@xxxxxxxxxxxx>

---
 fs/xfs/linux-2.6/xfs_buf.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

===================================================================
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -186,6 +186,19 @@ free_address(
        void            *addr)
 {
        a_list_t        *aentry;
+
+#ifdef CONFIG_XEN
+       /*
+        * Xen needs to be able to make sure it can get an exclusive
+        * RO mapping of pages it wants to turn into a pagetable.  If
+        * a newly allocated page is also still being vmap()ed by xfs,
+        * it will cause pagetable construction to fail.  This is a
+        * quick workaround to always eagerly unmap pages so that Xen
+        * is happy.
+        */
+       vunmap(addr);
+       return;
+#endif
 
        aentry = kmalloc(sizeof(a_list_t), GFP_NOWAIT);
        if (likely(aentry)) {

-- 


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel