[Xen-changelog] [xen-unstable] x86/mm/p2m: don't overwrite m2p entry of still-shared pages

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
# Date 1322148057 0
# Node ID f71ff2f7b604ff299c418854677880cac9d31f4f
# Parent  6b3d8250ee2c63d90680c142549123a4b1559f55
x86/mm/p2m: don't overwrite m2p entry of still-shared pages

When updating a p2m mapping to shared, previous code
unconditionally set the m2p entry for the old mfn to invalid.
We now check that the old mfn does not remain shared.

Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
Acked-by: Tim Deegan <tim@xxxxxxx>
Committed-by: Tim Deegan <tim@xxxxxxx>
---


diff -r 6b3d8250ee2c -r f71ff2f7b604 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Thu Nov 24 15:20:57 2011 +0000
+++ b/xen/arch/x86/mm/p2m.c     Thu Nov 24 15:20:57 2011 +0000
@@ -714,8 +714,9 @@
      * sharable first */
     ASSERT(p2m_is_shared(ot));
     ASSERT(mfn_valid(omfn));
-    /* XXX: M2P translations have to be handled properly for shared pages */
-    set_gpfn_from_mfn(mfn_x(omfn), INVALID_M2P_ENTRY);
+    if ( ((mfn_to_page(omfn)->u.inuse.type_info & PGT_type_mask) 
+                    != PGT_shared_page) )
+        set_gpfn_from_mfn(mfn_x(omfn), INVALID_M2P_ENTRY);
 
     P2M_DEBUG("set shared %lx %lx\n", gfn, mfn_x(mfn));
     rc = set_p2m_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2m_ram_shared, 
p2m->default_access);

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