[Xen-changelog] [xen-unstable] x86/mm: Make asserts on types and counts of shared pages more accurate

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Tim Deegan <tim@xxxxxxx>
# Date 1329406979 0
# Node ID 202db6f0907d06887d7bb7bbb708083f956bdce3
# Parent  01c1bcbc62224833304ede44187400f65e8a6b4c
x86/mm: Make asserts on types and counts of shared pages more accurate

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


diff -r 01c1bcbc6222 -r 202db6f0907d xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c     Thu Feb 16 08:48:23 2012 +0100
+++ b/xen/arch/x86/mm/mem_sharing.c     Thu Feb 16 15:42:59 2012 +0000
@@ -201,7 +201,9 @@
             /* Count has to be at least two, because we're called
              * with the mfn locked (1) and this is supposed to be 
              * a shared page (1). */
-            ASSERT((page->u.inuse.type_info & PGT_count_mask) >= 2); 
+            unsigned long t = read_atomic(&page->u.inuse.type_info);
+            ASSERT((t & PGT_type_mask) == PGT_shared_page);
+            ASSERT((t & PGT_count_mask) >= 2);
             ASSERT(get_gpfn_from_mfn(mfn) == SHARED_M2P_ENTRY); 
             return page;
         }
diff -r 01c1bcbc6222 -r 202db6f0907d xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Thu Feb 16 08:48:23 2012 +0100
+++ b/xen/arch/x86/mm/p2m.c     Thu Feb 16 15:42:59 2012 +0000
@@ -735,6 +735,7 @@
     p2m_access_t a;
     p2m_type_t ot;
     mfn_t omfn;
+    unsigned long pg_type;
 
     if ( !paging_mode_translate(p2m->domain) )
         return 0;
@@ -745,8 +746,11 @@
      * sharable first */
     ASSERT(p2m_is_shared(ot));
     ASSERT(mfn_valid(omfn));
-    if ( ((mfn_to_page(omfn)->u.inuse.type_info & PGT_type_mask) 
-                    != PGT_shared_page) )
+    /* Set the m2p entry to invalid only if there are no further type
+     * refs to this page as shared */
+    pg_type = read_atomic(&(mfn_to_page(omfn)->u.inuse.type_info));
+    if ( (pg_type & PGT_count_mask) == 0
+         || (pg_type & 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));

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