x86/mm: Make asserts on types and counts of shared pages more accurate

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Signed-off-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index 38ef870bf9789e49eabb2a098746abb1092a659f..36a50e58d48fbea79e4a87e6b7774095f5982701 100644 (file)
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -201,7 +201,9 @@ static struct page_info* mem_sharing_lookup(unsigned long mfn)
             /* 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 --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 233853b493e2f3b518883cac1f2d755b31fd53f3..fd1ef34a7362409c79677325811a259b0934f035 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -735,6 +735,7 @@ set_shared_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn)
     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 @@ set_shared_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn)
      * 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));