[PATCH v5 2/9] xen: do not free reserved memory into heap

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Pages used as guest RAM for static domain, shall be reserved to this
domain only.
So in case reserved pages being used for other purpose, users
shall not free them back to heap, even when last ref gets dropped.

free_staticmem_pages will be called by free_heap_pages in runtime
for static domain freeing memory resource, so let's drop the __init
flag.

Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
---
v5 changes:
- In order to avoid stub functions, we #define PGC_staticmem to non-zero only
when CONFIG_STATIC_MEMORY
- use "unlikely()" around pg->count_info & PGC_staticmem
- remove pointless "if", since mark_page_free() is going to set count_info
to PGC_state_free and by consequence clear PGC_staticmem
- move #define PGC_staticmem 0 to mm.h
---
v4 changes:
- no changes
---
v3 changes:
- fix possible racy issue in free_staticmem_pages()
- introduce a stub free_staticmem_pages() for the !CONFIG_STATIC_MEMORY case
- move the change to free_heap_pages() to cover other potential call sites
- fix the indentation
---
v2 changes:
- new commit
---
 xen/arch/arm/include/asm/mm.h |  2 ++
 xen/common/page_alloc.c       | 16 +++++++++-------
 xen/include/xen/mm.h          |  6 +++++-
 3 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 1226700085..56d0939318 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -108,9 +108,11 @@ struct page_info
   /* Page is Xen heap? */
 #define _PGC_xen_heap     PG_shift(2)
 #define PGC_xen_heap      PG_mask(1, 2)
+#ifdef CONFIG_STATIC_MEMORY
   /* Page is static memory */
 #define _PGC_staticmem    PG_shift(3)
 #define PGC_staticmem     PG_mask(1, 3)
+#endif
 /* ... */
 /* Page is broken? */
 #define _PGC_broken       PG_shift(7)
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 44600dd9cd..6425761116 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -151,10 +151,6 @@
 #define p2m_pod_offline_or_broken_replace(pg) BUG_ON(pg != NULL)
 #endif
 
-#ifndef PGC_staticmem
-#define PGC_staticmem 0
-#endif
-
 /*
  * Comma-separated list of hexadecimal page numbers containing bad bytes.
  * e.g. 'badpage=0x3f45,0x8a321'.
@@ -1443,6 +1439,13 @@ static void free_heap_pages(
 
     ASSERT(order <= MAX_ORDER);
 
+    if ( unlikely(pg->count_info & PGC_staticmem) )
+    {
+        /* Pages of static memory shall not go back to the heap. */
+        free_staticmem_pages(pg, 1UL << order, need_scrub);
+        return;
+    }
+
     spin_lock(&heap_lock);
 
     for ( i = 0; i < (1 << order); i++ )
@@ -2636,8 +2639,8 @@ struct domain *get_pg_owner(domid_t domid)
 
 #ifdef CONFIG_STATIC_MEMORY
 /* Equivalent of free_heap_pages to free nr_mfns pages of static memory. */
-void __init free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
-                                 bool need_scrub)
+void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
+                          bool need_scrub)
 {
     mfn_t mfn = page_to_mfn(pg);
     unsigned long i;
@@ -2652,7 +2655,6 @@ void __init free_staticmem_pages(struct page_info *pg, 
unsigned long nr_mfns,
             scrub_one_page(pg);
         }
 
-        /* In case initializing page of static memory, mark it PGC_staticmem. 
*/
         pg[i].count_info |= PGC_staticmem;
     }
 }
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 3be754da92..ca2c6f033e 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -85,10 +85,10 @@ bool scrub_free_pages(void);
 } while ( false )
 #define FREE_XENHEAP_PAGE(p) FREE_XENHEAP_PAGES(p, 0)
 
-#ifdef CONFIG_STATIC_MEMORY
 /* These functions are for static memory */
 void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
                           bool need_scrub);
+#ifdef CONFIG_STATIC_MEMORY
 int acquire_domstatic_pages(struct domain *d, mfn_t smfn, unsigned int nr_mfns,
                             unsigned int memflags);
 #endif
@@ -212,6 +212,10 @@ extern struct domain *dom_cow;
 
 #include <asm/mm.h>
 
+#ifndef PGC_staticmem
+#define PGC_staticmem 0
+#endif
+
 static inline bool is_special_page(const struct page_info *page)
 {
     return is_xen_heap_page(page) || (page->count_info & PGC_extra);
-- 
2.25.1