[Xen-devel] [PATCH] x86/mm: Make asserts on types and counts of shared pages more accurate

[Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>]

 xen/arch/x86/mm/mem_sharing.c |  4 +++-
 xen/arch/x86/mm/p2m.c         |  6 ++++--
 2 files changed, 7 insertions(+), 3 deletions(-)


Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

diff -r 667191f054c3 -r f2efbfaa8d26 xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -200,7 +200,9 @@ static struct page_info* mem_sharing_loo
             /* 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); 
+            ASSERT((page->u.inuse.type_info & 
+                        (PGT_shared_page | PGT_count_mask)) >= 
+                            (PGT_shared_page | 2)); 
             ASSERT(get_gpfn_from_mfn(mfn) == SHARED_M2P_ENTRY); 
             return page;
         }
diff -r 667191f054c3 -r f2efbfaa8d26 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -745,8 +745,10 @@ set_shared_p2m_entry(struct domain *d, u
      * 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 */
+    if ( (mfn_to_page(omfn)->u.inuse.type_info & 
+            (PGT_shared_page | PGT_count_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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