x86/mm: Allow foreign read-only mappings of shared pages

Because shared pages are owned by dom_cow, the ownership test
while foreign mapping fails.

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

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 2183bade3325a20592bd0a4135393b872da90108..fc954bb8e31851b5f1e193308ba3a61387e964c7 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -878,7 +878,8 @@ get_page_from_l1e(
         return 1;
     }
 
-    if ( unlikely(real_pg_owner != pg_owner) )
+    if ( unlikely( (real_pg_owner != pg_owner) &&
+                   (real_pg_owner != dom_cow) ) )
     {
         /*
          * Let privileged domains transfer the right to map their target
@@ -892,6 +893,11 @@ get_page_from_l1e(
         pg_owner = real_pg_owner;
     }
 
+    /* Extra paranoid check for shared memory. Writable mappings 
+     * disallowed (unshare first!) */
+    if ( (l1f & _PAGE_RW) && (real_pg_owner == dom_cow) )
+        goto could_not_pin;
+
     /* Foreign mappings into guests in shadow external mode don't
      * contribute to writeable mapping refcounts.  (This allows the
      * qemu-dm helper process in dom0 to map the domain's memory without