[Xen-changelog] [xen-unstable] x86/mm: Allow foreign read-only mappings of shared pages

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
# Date 1327584087 0
# Node ID 1aa50ddb605a179b7321844d8e31b6ea29cbd0f7
# Parent  f6c33cfe7333a12f6792e6ce15ddf70818508cea
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@xxxxxxxxxxxxxxxx>
Acked-by: Tim Deegan <tim@xxxxxxx>
Committed-by: Tim Deegan <tim@xxxxxxx>
---


diff -r f6c33cfe7333 -r 1aa50ddb605a xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c Thu Jan 26 13:21:27 2012 +0000
+++ b/xen/arch/x86/mm.c Thu Jan 26 13:21:27 2012 +0000
@@ -878,7 +878,8 @@
         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 @@
         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

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