[Xen-devel] [PATCH v1 9/9] mm: Make sure pages are scrubbed

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Add a debug Kconfig option that will make page allocator verify
that pages that were supposed to be scrubbed are, in fact, clean.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/Kconfig.debug       |    7 +++++++
 xen/common/page_alloc.c |   33 +++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 0 deletions(-)

diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
index 8139564..35b86ae 100644
--- a/xen/Kconfig.debug
+++ b/xen/Kconfig.debug
@@ -113,6 +113,13 @@ config DEVICE_TREE_DEBUG
          logged in the Xen ring buffer.
          If unsure, say N here.
 
+config SCRUB_DEBUG
+       bool "Page scrubbing test"
+       default y
+       ---help---
+          Verify that pages that need to be scrubbed before being allocated to
+         a guest are indeed scrubbed.
+
 endif # DEBUG || EXPERT
 
 endmenu
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 7dfbd8c..8140446 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -685,6 +685,29 @@ static void check_low_mem_virq(void)
     }
 }
 
+#ifdef CONFIG_SCRUB_DEBUG
+#define PAGE_POISON 0xbad0bad0bad0bad0ULL
+static void poison_one_page(struct page_info *pg)
+{
+    mfn_t mfn = _mfn(page_to_mfn(pg));
+    uint64_t *ptr;
+
+    ptr  = map_domain_page(mfn);
+    *ptr = PAGE_POISON;
+    unmap_domain_page(ptr);
+}
+
+static void check_one_page(struct page_info *pg)
+{
+    mfn_t mfn = _mfn(page_to_mfn(pg));
+    uint64_t *ptr;
+
+    ptr  = map_domain_page(mfn);
+    ASSERT(*ptr != PAGE_POISON);
+    unmap_domain_page(ptr);
+}
+#endif /* CONFIG_SCRUB_DEBUG */
+
 static void check_and_stop_scrub(struct page_info *head)
 {
     if ( head->u.free.scrub_state & PAGE_SCRUBBING )
@@ -905,6 +928,11 @@ static struct page_info *alloc_heap_pages(
          * guest can control its own visibility of/through the cache.
          */
         flush_page_to_ram(page_to_mfn(&pg[i]));
+
+#ifdef CONFIG_SCRUB_DEBUG
+        if ( d && !is_idle_domain(d) )
+            check_one_page(&pg[i]);
+#endif
     }
 
     spin_unlock(&heap_lock);
@@ -1285,6 +1313,11 @@ static void free_heap_pages(
     {
         pg->count_info |= PGC_need_scrub;
         node_need_scrub[node] += (1UL << order);
+
+#ifdef CONFIG_SCRUB_DEBUG
+        for ( i = 0; i < (1 << order); i++ )
+            poison_one_page(&pg[i]);
+#endif
     }
 
     merge_chunks(pg, node, zone, order, 0);
-- 
1.7.1


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