diff -r 6472342c8ab0 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c	Wed Sep 30 08:51:21 2009 +0100
+++ b/xen/arch/x86/mm/p2m.c	Wed Sep 30 10:04:23 2009 +0100
@@ -2216,10 +2216,12 @@
     if ( !paging_mode_translate(d) )
         return 0;
 
+    p2m_lock(d->arch.p2m);
     omfn = gfn_to_mfn_query(d, gfn, &ot);
     if ( p2m_is_grant(ot) )
     {
         domain_crash(d);
+        p2m_unlock(d->arch.p2m);
         return 0;
     }
     else if ( p2m_is_ram(ot) )
@@ -2234,6 +2236,8 @@
         gdprintk(XENLOG_ERR,
             "set_mmio_p2m_entry: set_p2m_entry failed! mfn=%08lx\n",
             gmfn_to_mfn(d, gfn));
+
+    p2m_unlock(d->arch.p2m);
     return rc;
 }
 
@@ -2246,14 +2250,17 @@
     if ( !paging_mode_translate(d) )
         return 0;
 
+    p2m_lock(d->arch.p2m);
     mfn = gmfn_to_mfn(d, gfn);
     if ( INVALID_MFN == mfn )
     {
         gdprintk(XENLOG_ERR,
             "clear_mmio_p2m_entry: gfn_to_mfn failed! gfn=%08lx\n", gfn);
+        p2m_unlock(d->arch.p2m);
         return 0;
     }
     rc = set_p2m_entry(d, gfn, _mfn(INVALID_MFN), 0, 0);
+    p2m_unlock(d->arch.p2m);
 
     return rc;
 }