shadow: fix the fix for promotion/resync race.

Signed-off-by: Gianluca Guida <gianluca.guida@eu.citrix.com>
xen-unstable changeset:   18841:9be2fe3de5678320ff4718daaee11be6ddb67cf2
xen-unstable date:        Fri Nov 28 12:02:43 2008 +0000

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index d07dde12d9e6829480c0846b2064df2435c64e22..7cb734a31f9b3d6ee8529f5000d9cd41fb03f801 100644 (file)
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -2182,13 +2182,6 @@ static shadow_l1e_t * shadow_get_and_create_l1e(struct vcpu *v,
         if ( r & SHADOW_SET_ERROR )
             return NULL;
 
-#if (SHADOW_OPTIMIZATIONS && SHOPT_OUT_OF_SYNC )
-        /* All pages walked are now pagetables. Safe to resync pages
-           in case level 4 or 3 shadows were set. */
-        if ( resync )
-            shadow_resync_all(v, 0);
-#endif
-
         /* This next line is important: in 32-on-PAE and 32-on-64 modes,
          * the guest l1 table has an 8k shadow, and we need to return
          * the right mfn of the pair. This call will set it for us as a
@@ -2196,6 +2189,14 @@ static shadow_l1e_t * shadow_get_and_create_l1e(struct vcpu *v,
          * compiled out.) */
         (void) shadow_l1_index(sl1mfn, guest_l1_table_offset(gw->va));
     }
+
+#if (SHADOW_OPTIMIZATIONS && SHOPT_OUT_OF_SYNC )
+    /* All pages walked are now pagetables. Safe to resync pages
+       in case level 4 or 3 shadows were set. */
+    if ( resync )
+        shadow_resync_all(v, 0);
+#endif
+
     /* Now follow it down a level.  Guaranteed to succeed. */
     return sh_linear_l1_table(v) + shadow_l1_linear_offset(gw->va);
 }
@@ -2472,7 +2473,8 @@ static int validate_gl4e(struct vcpu *v, void *new_ge, mfn_t sl4mfn, void *se)
             result |= SHADOW_SET_ERROR;
 
 #if (SHADOW_OPTIMIZATIONS && SHOPT_OUT_OF_SYNC )
-        shadow_resync_all(v, 0);
+        if ( mfn_valid(sl3mfn) )
+            shadow_resync_all(v, 0);
 #endif
     }
     l4e_propagate_from_guest(v, new_gl4e, sl3mfn, &new_sl4e, ft_prefetch);
@@ -2528,7 +2530,8 @@ static int validate_gl3e(struct vcpu *v, void *new_ge, mfn_t sl3mfn, void *se)
             result |= SHADOW_SET_ERROR;
 
 #if (SHADOW_OPTIMIZATIONS && SHOPT_OUT_OF_SYNC )
-        shadow_resync_all(v, 0);
+        if ( mfn_valid(sl2mfn) )
+            shadow_resync_all(v, 0);
 #endif
     }
     l3e_propagate_from_guest(v, new_gl3e, sl2mfn, &new_sl3e, ft_prefetch);