page-vary: Move and rename qemu_target_page_bits_min

Rename to migration_legacy_page_bits, to make it clear that
we cannot change the value without causing a migration break.
Move to page-vary.h and page-vary-target.c.
Define via TARGET_PAGE_BITS if not TARGET_PAGE_BITS_VARY.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/exec/page-vary.h

@@ -49,4 +49,13 @@ bool set_preferred_target_page_bits(int bits);
  */
 void finalize_target_page_bits(void);
 
+/**
+ * migration_legacy_page_bits
+ *
+ * For migration compatibility with qemu v2.9, prior to the introduction
+ * of the configuration/target-page-bits section, return the value of
+ * TARGET_PAGE_BITS that the target had then.
+ */
+int migration_legacy_page_bits(void);
+
 #endif /* EXEC_PAGE_VARY_H */

include/exec/target_page.h

@@ -63,7 +63,6 @@ static inline int qemu_target_page_bits(void)
     return TARGET_PAGE_BITS;
 }
 
-int qemu_target_page_bits_min(void);
 size_t qemu_target_pages_to_MiB(size_t pages);
 
 #endif

migration/savevm.c

@@ -50,6 +50,7 @@
 #include "system/cpus.h"
 #include "system/memory.h"
 #include "exec/target_page.h"
+#include "exec/page-vary.h"
 #include "trace.h"
 #include "qemu/iov.h"
 #include "qemu/job.h"
@@ -339,7 +340,7 @@ static int configuration_pre_load(void *opaque)
      * predates the variable-target-page-bits support and is using the
      * minimum possible value for this CPU.
      */
-    state->target_page_bits = qemu_target_page_bits_min();
+    state->target_page_bits = migration_legacy_page_bits();
     return 0;
 }
 
@@ -462,8 +463,7 @@ static const VMStateInfo vmstate_info_capability = {
  */
 static bool vmstate_target_page_bits_needed(void *opaque)
 {
-    return qemu_target_page_bits()
+    return qemu_target_page_bits() > migration_legacy_page_bits();
-        > qemu_target_page_bits_min();
 }
 
 static const VMStateDescription vmstate_target_page_bits = {

page-target.c

@@ -9,11 +9,6 @@
 #include "qemu/osdep.h"
 #include "exec/target_page.h"
 
-int qemu_target_page_bits_min(void)
-{
-    return TARGET_PAGE_BITS_MIN;
-}
-
 /* Convert target pages to MiB (2**20). */
 size_t qemu_target_pages_to_MiB(size_t pages)
 {

page-vary-target.c

@@ -23,6 +23,15 @@
 #include "exec/page-vary.h"
 #include "exec/target_page.h"
 
+int migration_legacy_page_bits(void)
+{
+#ifdef TARGET_PAGE_BITS_VARY
+    return TARGET_PAGE_BITS_MIN;
+#else
+    return TARGET_PAGE_BITS;
+#endif
+}
+
 bool set_preferred_target_page_bits(int bits)
 {
 #ifdef TARGET_PAGE_BITS_VARY