migration/multifd: Add new migration option zero-page-detection.

This new parameter controls where the zero page checking is running.
1. If this parameter is set to 'legacy', zero page checking is
done in the migration main thread.
2. If this parameter is set to 'none', zero page checking is disabled.

Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Link: https://lore.kernel.org/r/20240311180015.3359271-4-hao.xiang@linux.dev
Signed-off-by: Peter Xu <peterx@redhat.com>

hw/core/qdev-properties-system.c

@@ -693,6 +693,16 @@ const PropertyInfo qdev_prop_granule_mode = {
     .set_default_value = qdev_propinfo_set_default_value_enum,
 };
 
+const PropertyInfo qdev_prop_zero_page_detection = {
+    .name = "ZeroPageDetection",
+    .description = "zero_page_detection values, "
+                   "none,legacy",
+    .enum_table = &ZeroPageDetection_lookup,
+    .get = qdev_propinfo_get_enum,
+    .set = qdev_propinfo_set_enum,
+    .set_default_value = qdev_propinfo_set_default_value_enum,
+};
+
 /* --- Reserved Region --- */
 
 /*

include/hw/qdev-properties-system.h

@@ -9,6 +9,7 @@ extern const PropertyInfo qdev_prop_reserved_region;
 extern const PropertyInfo qdev_prop_multifd_compression;
 extern const PropertyInfo qdev_prop_mig_mode;
 extern const PropertyInfo qdev_prop_granule_mode;
+extern const PropertyInfo qdev_prop_zero_page_detection;
 extern const PropertyInfo qdev_prop_losttickpolicy;
 extern const PropertyInfo qdev_prop_blockdev_on_error;
 extern const PropertyInfo qdev_prop_bios_chs_trans;
@@ -50,6 +51,9 @@ extern const PropertyInfo qdev_prop_iothread_vq_mapping_list;
                        MigMode)
 #define DEFINE_PROP_GRANULE_MODE(_n, _s, _f, _d) \
     DEFINE_PROP_SIGNED(_n, _s, _f, _d, qdev_prop_granule_mode, GranuleMode)
+#define DEFINE_PROP_ZERO_PAGE_DETECTION(_n, _s, _f, _d) \
+    DEFINE_PROP_SIGNED(_n, _s, _f, _d, qdev_prop_zero_page_detection, \
+                       ZeroPageDetection)
 #define DEFINE_PROP_LOSTTICKPOLICY(_n, _s, _f, _d) \
     DEFINE_PROP_SIGNED(_n, _s, _f, _d, qdev_prop_losttickpolicy, \
                         LostTickPolicy)

migration/migration-hmp-cmds.c

@@ -344,6 +344,11 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "%s: %s\n",
             MigrationParameter_str(MIGRATION_PARAMETER_MULTIFD_COMPRESSION),
             MultiFDCompression_str(params->multifd_compression));
+        assert(params->has_zero_page_detection);
+        monitor_printf(mon, "%s: %s\n",
+            MigrationParameter_str(MIGRATION_PARAMETER_ZERO_PAGE_DETECTION),
+            qapi_enum_lookup(&ZeroPageDetection_lookup,
+                params->zero_page_detection));
         monitor_printf(mon, "%s: %" PRIu64 " bytes\n",
             MigrationParameter_str(MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE),
             params->xbzrle_cache_size);
@@ -634,6 +639,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
         p->has_multifd_zstd_level = true;
         visit_type_uint8(v, param, &p->multifd_zstd_level, &err);
         break;
+    case MIGRATION_PARAMETER_ZERO_PAGE_DETECTION:
+        p->has_zero_page_detection = true;
+        visit_type_ZeroPageDetection(v, param, &p->zero_page_detection, &err);
+        break;
     case MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE:
         p->has_xbzrle_cache_size = true;
         if (!visit_type_size(v, param, &cache_size, &err)) {

migration/options.c

@@ -179,6 +179,9 @@ Property migration_properties[] = {
     DEFINE_PROP_MIG_MODE("mode", MigrationState,
                       parameters.mode,
                       MIG_MODE_NORMAL),
+    DEFINE_PROP_ZERO_PAGE_DETECTION("zero-page-detection", MigrationState,
+                       parameters.zero_page_detection,
+                       ZERO_PAGE_DETECTION_LEGACY),
 
     /* Migration capabilities */
     DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
@@ -938,6 +941,13 @@ uint64_t migrate_xbzrle_cache_size(void)
     return s->parameters.xbzrle_cache_size;
 }
 
+ZeroPageDetection migrate_zero_page_detection(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return s->parameters.zero_page_detection;
+}
+
 /* parameter setters */
 
 void migrate_set_block_incremental(bool value)
@@ -1048,6 +1058,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->vcpu_dirty_limit = s->parameters.vcpu_dirty_limit;
     params->has_mode = true;
     params->mode = s->parameters.mode;
+    params->has_zero_page_detection = true;
+    params->zero_page_detection = s->parameters.zero_page_detection;
 
     return params;
 }
@@ -1084,6 +1096,7 @@ void migrate_params_init(MigrationParameters *params)
     params->has_x_vcpu_dirty_limit_period = true;
     params->has_vcpu_dirty_limit = true;
     params->has_mode = true;
+    params->has_zero_page_detection = true;
 }
 
 /*
@@ -1398,6 +1411,10 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_mode) {
         dest->mode = params->mode;
     }
+
+    if (params->has_zero_page_detection) {
+        dest->zero_page_detection = params->zero_page_detection;
+    }
 }
 
 static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1548,6 +1565,10 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_mode) {
         s->parameters.mode = params->mode;
     }
+
+    if (params->has_zero_page_detection) {
+        s->parameters.zero_page_detection = params->zero_page_detection;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)

migration/options.h

@@ -90,6 +90,7 @@ const char *migrate_tls_authz(void);
 const char *migrate_tls_creds(void);
 const char *migrate_tls_hostname(void);
 uint64_t migrate_xbzrle_cache_size(void);
+ZeroPageDetection migrate_zero_page_detection(void);
 
 /* parameters setters */
 

migration/ram.c

@@ -1140,6 +1140,10 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss,
     QEMUFile *file = pss->pss_channel;
     int len = 0;
 
+    if (migrate_zero_page_detection() == ZERO_PAGE_DETECTION_NONE) {
+        return 0;
+    }
+
     if (!buffer_is_zero(p, TARGET_PAGE_SIZE)) {
         return 0;
     }

qapi/migration.json

@@ -670,6 +670,18 @@
 { 'enum': 'MigMode',
   'data': [ 'normal', 'cpr-reboot' ] }
 
+##
+# @ZeroPageDetection:
+#
+# @none: Do not perform zero page checking.
+#
+# @legacy: Perform zero page checking in main migration thread.
+#
+# Since: 9.0
+##
+{ 'enum': 'ZeroPageDetection',
+  'data': [ 'none', 'legacy' ] }
+
 ##
 # @BitmapMigrationBitmapAliasTransform:
 #
@@ -891,6 +903,10 @@
 # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
 #        (Since 8.2)
 #
+# @zero-page-detection: Whether and how to detect zero pages.
+#     See description in @ZeroPageDetection.  Default is 'legacy'.
+#     (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -924,7 +940,8 @@
            'block-bitmap-mapping',
            { 'name': 'x-vcpu-dirty-limit-period', 'features': ['unstable'] },
            'vcpu-dirty-limit',
-           'mode'] }
+           'mode',
+           'zero-page-detection'] }
 
 ##
 # @MigrateSetParameters:
@@ -1083,6 +1100,10 @@
 # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
 #        (Since 8.2)
 #
+# @zero-page-detection: Whether and how to detect zero pages.
+#     See description in @ZeroPageDetection.  Default is 'legacy'.
+#     (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -1136,7 +1157,8 @@
             '*x-vcpu-dirty-limit-period': { 'type': 'uint64',
                                             'features': [ 'unstable' ] },
             '*vcpu-dirty-limit': 'uint64',
-            '*mode': 'MigMode'} }
+            '*mode': 'MigMode',
+            '*zero-page-detection': 'ZeroPageDetection'} }
 
 ##
 # @migrate-set-parameters:
@@ -1311,6 +1333,10 @@
 # @mode: Migration mode. See description in @MigMode. Default is 'normal'.
 #        (Since 8.2)
 #
+# @zero-page-detection: Whether and how to detect zero pages.
+#     See description in @ZeroPageDetection.  Default is 'legacy'.
+#     (since 9.0)
+#
 # Features:
 #
 # @deprecated: Member @block-incremental is deprecated.  Use
@@ -1361,7 +1387,8 @@
             '*x-vcpu-dirty-limit-period': { 'type': 'uint64',
                                             'features': [ 'unstable' ] },
             '*vcpu-dirty-limit': 'uint64',
-            '*mode': 'MigMode'} }
+            '*mode': 'MigMode',
+            '*zero-page-detection': 'ZeroPageDetection'} }
 
 ##
 # @query-migrate-parameters: