x86: paging_log_dirty_op() should take care with invalid log_dirty.top

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 2b898dd73b6c18633e4bfcdbc62046af826f34ff..0df7376c24d5c6e160db020659d7d590d6623ef4 100644 (file)
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -385,13 +385,14 @@ int paging_log_dirty_op(struct domain *d, struct xen_domctl_shadow_op *sc)
     }
 
     pages = 0;
-    l4 = map_domain_page(mfn_x(d->arch.paging.log_dirty.top));
+    l4 = (mfn_valid(d->arch.paging.log_dirty.top) ?
+          map_domain_page(mfn_x(d->arch.paging.log_dirty.top)) : NULL);
 
     for ( i4 = 0;
           (pages < sc->pages) && (i4 < LOGDIRTY_NODE_ENTRIES);
           i4++ )
     {
-        l3 = mfn_valid(l4[i4]) ? map_domain_page(mfn_x(l4[i4])) : NULL;
+        l3 = (l4 && mfn_valid(l4[i4])) ? map_domain_page(mfn_x(l4[i4])) : NULL;
         for ( i3 = 0;
               (pages < sc->pages) && (i3 < LOGDIRTY_NODE_ENTRIES);
               i3++ )