PoD: Scrub pages before adding to the cache

Neither memory from the allocator nor memory from
the balloon driver is guaranteed to be zero.  Scrub it
before adding to the cache.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index cc0653fa7ea5043c7586cb7395cba4127559709a..15c6b921be337c106c8af8b90488f3017c508780 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -307,6 +307,17 @@ p2m_pod_cache_add(struct domain *d,
     }
 #endif
 
+    /* Pages from domain_alloc and returned by the balloon driver aren't
+     * guaranteed to be zero; but by reclaiming zero pages, we implicitly promise
+     * to provide zero pages.  So we scrub pages before using */
+    for ( i=0; i< 1 << order ; i++)
+    {
+        char * b;
+        b = map_domain_page(page_to_mfn(page) + i);
+        clear_page(b);
+        unmap_domain_page(b);
+    }
+
     spin_lock(&d->page_alloc_lock);
 
     /* First, take all pages off the domain list */