xen: introduce prepare_staticmem_pages

Later, we want to use acquire_domstatic_pages() for populating memory
for static domain on runtime, however, there are a lot of pointless work
(checking mfn_valid(), scrubbing the free part, cleaning the cache...)
considering we know the page is valid and belong to the guest.

This commit splits acquire_staticmem_pages() in two parts, and
introduces prepare_staticmem_pages to bypass all "pointless work".

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/common/page_alloc.c

@@ -2752,26 +2752,13 @@ void free_domstatic_page(struct page_info *page)
         put_domain(d);
 }
 
-/*
- * Acquire nr_mfns contiguous reserved pages, starting at #smfn, of
- * static memory.
- * This function needs to be reworked if used outside of boot.
- */
-static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
-                                                         unsigned long nr_mfns,
-                                                         unsigned int memflags)
+static bool __init prepare_staticmem_pages(struct page_info *pg,
+                                           unsigned long nr_mfns,
+                                           unsigned int memflags)
 {
     bool need_tlbflush = false;
     uint32_t tlbflush_timestamp = 0;
     unsigned long i;
-    struct page_info *pg;
-
-    ASSERT(nr_mfns);
-    for ( i = 0; i < nr_mfns; i++ )
-        if ( !mfn_valid(mfn_add(smfn, i)) )
-            return NULL;
-
-    pg = mfn_to_page(smfn);
 
     spin_lock(&heap_lock);
 
@@ -2782,7 +2769,7 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
         {
             printk(XENLOG_ERR
                    "pg[%lu] Static MFN %"PRI_mfn" c=%#lx t=%#x\n",
-                   i, mfn_x(smfn) + i,
+                   i, mfn_x(page_to_mfn(pg)) + i,
                    pg[i].count_info, pg[i].tlbflush_timestamp);
             goto out_err;
         }
@@ -2806,6 +2793,38 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
     if ( need_tlbflush )
         filtered_flush_tlb_mask(tlbflush_timestamp);
 
+    return true;
+
+ out_err:
+    while ( i-- )
+        pg[i].count_info = PGC_static | PGC_state_free;
+
+    spin_unlock(&heap_lock);
+
+    return false;
+}
+
+/*
+ * Acquire nr_mfns contiguous reserved pages, starting at #smfn, of
+ * static memory.
+ * This function needs to be reworked if used outside of boot.
+ */
+static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
+                                                         unsigned long nr_mfns,
+                                                         unsigned int memflags)
+{
+    unsigned long i;
+    struct page_info *pg;
+
+    ASSERT(nr_mfns);
+    for ( i = 0; i < nr_mfns; i++ )
+        if ( !mfn_valid(mfn_add(smfn, i)) )
+            return NULL;
+
+    pg = mfn_to_page(smfn);
+    if ( !prepare_staticmem_pages(pg, nr_mfns, memflags) )
+        return NULL;
+
     /*
      * Ensure cache and RAM are consistent for platforms where the guest
      * can control its own visibility of/through the cache.
@@ -2814,14 +2833,6 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn,
         flush_page_to_ram(mfn_x(smfn) + i, !(memflags & MEMF_no_icache_flush));
 
     return pg;
-
- out_err:
-    while ( i-- )
-        pg[i].count_info = PGC_static | PGC_state_free;
-
-    spin_unlock(&heap_lock);
-
-    return NULL;
 }
 
 /*