page-alloc: make scrub_one_page() static

Before starting to alter its properties, restrict the function's
visibility. The only external user is mem-paging, which we can
accommodate by different means.

Also move the function up in its source file, so we won't need to
forward-declare it. Constify its parameter at the same time.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/arch/x86/include/asm/mem_paging.h

@@ -12,12 +12,6 @@
 
 int mem_paging_memop(XEN_GUEST_HANDLE_PARAM(xen_mem_paging_op_t) arg);
 
-#ifdef CONFIG_MEM_PAGING
-# define mem_paging_enabled(d) vm_event_check_ring((d)->vm_event_paging)
-#else
-# define mem_paging_enabled(d) false
-#endif
-
 #endif /*__ASM_X86_MEM_PAGING_H__ */
 
 /*

xen/arch/x86/mm/mem_paging.c

@@ -304,9 +304,6 @@ static int evict(struct domain *d, gfn_t gfn)
     ret = p2m_set_entry(p2m, gfn, INVALID_MFN, PAGE_ORDER_4K,
                         p2m_ram_paged, a);
 
-    /* Clear content before returning the page to Xen */
-    scrub_one_page(page);
-
     /* Track number of paged gfns */
     atomic_inc(&d->paged_pages);
 

xen/common/page_alloc.c

@@ -137,6 +137,7 @@
 #include <xen/sections.h>
 #include <xen/softirq.h>
 #include <xen/spinlock.h>
+#include <xen/vm_event.h>
 
 #include <asm/flushtlb.h>
 #include <asm/page.h>
@@ -774,6 +775,21 @@ static void page_list_add_scrub(struct page_info *pg, unsigned int node,
 #endif
 #define SCRUB_BYTE_PATTERN   (SCRUB_PATTERN & 0xff)
 
+static void scrub_one_page(const struct page_info *pg)
+{
+    if ( unlikely(pg->count_info & PGC_broken) )
+        return;
+
+#ifndef NDEBUG
+    /* Avoid callers relying on allocations returning zeroed pages. */
+    unmap_domain_page(memset(__map_domain_page(pg),
+                             SCRUB_BYTE_PATTERN, PAGE_SIZE));
+#else
+    /* For a production build, clear_page() is the fastest way to scrub. */
+    clear_domain_page(_mfn(page_to_mfn(pg)));
+#endif
+}
+
 static void poison_one_page(struct page_info *pg)
 {
 #ifdef CONFIG_SCRUB_DEBUG
@@ -2548,10 +2564,12 @@ void free_domheap_pages(struct page_info *pg, unsigned int order)
             /*
              * Normally we expect a domain to clear pages before freeing them,
              * if it cares about the secrecy of their contents. However, after
-             * a domain has died we assume responsibility for erasure. We do
-             * scrub regardless if option scrub_domheap is set.
+             * a domain has died or if it has mem-paging enabled we assume
+             * responsibility for erasure. We do scrub regardless if option
+             * scrub_domheap is set.
              */
-            scrub = d->is_dying || scrub_debug || opt_scrub_domheap;
+            scrub = d->is_dying || mem_paging_enabled(d) ||
+                    scrub_debug || opt_scrub_domheap;
         }
         else
         {
@@ -2635,22 +2653,6 @@ static __init int cf_check pagealloc_keyhandler_init(void)
 }
 __initcall(pagealloc_keyhandler_init);
 
-
-void scrub_one_page(struct page_info *pg)
-{
-    if ( unlikely(pg->count_info & PGC_broken) )
-        return;
-
-#ifndef NDEBUG
-    /* Avoid callers relying on allocations returning zeroed pages. */
-    unmap_domain_page(memset(__map_domain_page(pg),
-                             SCRUB_BYTE_PATTERN, PAGE_SIZE));
-#else
-    /* For a production build, clear_page() is the fastest way to scrub. */
-    clear_domain_page(_mfn(page_to_mfn(pg)));
-#endif
-}
-
 static void cf_check dump_heap(unsigned char key)
 {
     s_time_t      now = NOW();

xen/include/xen/mm.h

@@ -532,8 +532,6 @@ static inline unsigned int get_order_from_pages(unsigned long nr_pages)
     return order;
 }
 
-void scrub_one_page(struct page_info *pg);
-
 #ifndef arch_free_heap_page
 #define arch_free_heap_page(d, pg) \
     page_list_del(pg, page_to_list(d, pg))

xen/include/xen/sched.h

@@ -1203,6 +1203,12 @@ static always_inline bool is_iommu_enabled(const struct domain *d)
     return evaluate_nospec(d->options & XEN_DOMCTL_CDF_iommu);
 }
 
+#ifdef CONFIG_MEM_PAGING
+# define mem_paging_enabled(d) vm_event_check_ring((d)->vm_event_paging)
+#else
+# define mem_paging_enabled(d) false
+#endif
+
 extern bool sched_smt_power_savings;
 extern bool sched_disable_smt_switching;