[Xen-changelog] [xen-unstable] x86 shadow: Avoid remove-all-shadows after shadow teardown

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1274857281 -3600
# Node ID 5addb6cb16fd64c664b1e3dd335c76b3426e05e9
# Parent  459f35d8cac4f19e6eae0a7396f6c97e20ae955c
x86 shadow: Avoid remove-all-shadows after shadow teardown

If dom0 alters the p2m of a domain that's being destroyed, we can end
up doing a remove-all-shadows after the shadow hash table has been
freed. Since no hash table implies no shadows, just return
immediately.

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
---
 xen/arch/x86/mm/shadow/common.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletion(-)

diff -r 459f35d8cac4 -r 5addb6cb16fd xen/arch/x86/mm/shadow/common.c
--- a/xen/arch/x86/mm/shadow/common.c   Wed May 26 07:59:52 2010 +0100
+++ b/xen/arch/x86/mm/shadow/common.c   Wed May 26 08:01:21 2010 +0100
@@ -2173,8 +2173,13 @@ static void hash_foreach(struct vcpu *v,
     struct domain *d = v->domain;
     struct page_info *x;
 
+    ASSERT(shadow_locked_by_me(d));
+
+    /* Can be called via p2m code &c after shadow teardown. */
+    if ( unlikely(!d->arch.paging.shadow.hash_table) )
+        return;
+
     /* Say we're here, to stop hash-lookups reordering the chains */
-    ASSERT(shadow_locked_by_me(d));
     ASSERT(d->arch.paging.shadow.hash_walking == 0);
     d->arch.paging.shadow.hash_walking = 1;
 

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