migration/postcopy: enable random order target page arrival

After using number of target page received to track one host page, we
could have the capability to handle random order target page arrival in
one host page.

This is a preparation for enabling compress during postcopy.
Signed-off-by: NWei Yang <richardw.yang@linux.intel.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

migration/ram.c

@@ -4050,7 +4050,7 @@ static int ram_load_postcopy(QEMUFile *f)
     MigrationIncomingState *mis = migration_incoming_get_current();
     /* Temporary page that is later 'placed' */
     void *postcopy_host_page = mis->postcopy_tmp_page;
-    void *last_host = NULL;
+    void *this_host = NULL;
     bool all_zero = false;
     int target_pages = 0;
 
@@ -4097,24 +4097,26 @@ static int ram_load_postcopy(QEMUFile *f)
              * that's moved into place later.
              * The migration protocol uses,  possibly smaller, target-pages
              * however the source ensures it always sends all the components
-             * of a host page in order.
+             * of a host page in one chunk.
              */
             page_buffer = postcopy_host_page +
                           ((uintptr_t)host & (block->page_size - 1));
             /* If all TP are zero then we can optimise the place */
             if (target_pages == 1) {
                 all_zero = true;
+                this_host = (void *)QEMU_ALIGN_DOWN((uintptr_t)host,
+                                                    block->page_size);
             } else {
                 /* not the 1st TP within the HP */
-                if (host != (last_host + TARGET_PAGE_SIZE)) {
-                    error_report("Non-sequential target page %p/%p",
-                                  host, last_host);
+                if (QEMU_ALIGN_DOWN((uintptr_t)host, block->page_size) !=
+                    (uintptr_t)this_host) {
+                    error_report("Non-same host page %p/%p",
+                                  host, this_host);
                     ret = -EINVAL;
                     break;
                 }
             }
 
-
             /*
              * If it's the last part of a host page then we place the host
              * page
@@ -4125,7 +4127,6 @@ static int ram_load_postcopy(QEMUFile *f)
             }
             place_source = postcopy_host_page;
         }
-        last_host = host;
 
         switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
         case RAM_SAVE_FLAG_ZERO:
@@ -4178,7 +4179,8 @@ static int ram_load_postcopy(QEMUFile *f)
 
         if (!ret && place_needed) {
             /* This gets called at the last target page in the host page */
-            void *place_dest = host + TARGET_PAGE_SIZE - block->page_size;
+            void *place_dest = (void *)QEMU_ALIGN_DOWN((uintptr_t)host,
+                                                       block->page_size);
 
             if (all_zero) {
                 ret = postcopy_place_page_zero(mis, place_dest,