[PULL 12/16] migration: Add zero-copy-send parameter for QMP/HMP for Linux

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Leonardo Bras <leobras@redhat.com>

Add property that allows zero-copy migration of memory pages
on the sending side, and also includes a helper function
migrate_use_zero_copy_send() to check if it's enabled.

No code is introduced to actually do the migration, but it allow
future implementations to enable/disable this feature.

On non-Linux builds this parameter is compiled-out.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220507015759.840466-4-leobras@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  dgilbert: Removed accidental skibootism
---
 migration/migration.c | 32 ++++++++++++++++++++++++++++++++
 migration/migration.h |  5 +++++
 migration/socket.c    | 11 +++++++++--
 monitor/hmp-cmds.c    |  6 ++++++
 qapi/migration.json   | 24 ++++++++++++++++++++++++
 5 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 5a31b23bd6..3e91f4b5e2 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -910,6 +910,10 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->multifd_zlib_level = s->parameters.multifd_zlib_level;
     params->has_multifd_zstd_level = true;
     params->multifd_zstd_level = s->parameters.multifd_zstd_level;
+#ifdef CONFIG_LINUX
+    params->has_zero_copy_send = true;
+    params->zero_copy_send = s->parameters.zero_copy_send;
+#endif
     params->has_xbzrle_cache_size = true;
     params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
     params->has_max_postcopy_bandwidth = true;
@@ -1567,6 +1571,11 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_multifd_compression) {
         dest->multifd_compression = params->multifd_compression;
     }
+#ifdef CONFIG_LINUX
+    if (params->has_zero_copy_send) {
+        dest->zero_copy_send = params->zero_copy_send;
+    }
+#endif
     if (params->has_xbzrle_cache_size) {
         dest->xbzrle_cache_size = params->xbzrle_cache_size;
     }
@@ -1679,6 +1688,11 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_multifd_compression) {
         s->parameters.multifd_compression = params->multifd_compression;
     }
+#ifdef CONFIG_LINUX
+    if (params->has_zero_copy_send) {
+        s->parameters.zero_copy_send = params->zero_copy_send;
+    }
+#endif
     if (params->has_xbzrle_cache_size) {
         s->parameters.xbzrle_cache_size = params->xbzrle_cache_size;
         xbzrle_cache_resize(params->xbzrle_cache_size, errp);
@@ -2563,6 +2577,17 @@ int migrate_multifd_zstd_level(void)
     return s->parameters.multifd_zstd_level;
 }
 
+#ifdef CONFIG_LINUX
+bool migrate_use_zero_copy_send(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.zero_copy_send;
+}
+#endif
+
 int migrate_use_xbzrle(void)
 {
     MigrationState *s;
@@ -4206,6 +4231,10 @@ static Property migration_properties[] = {
     DEFINE_PROP_UINT8("multifd-zstd-level", MigrationState,
                       parameters.multifd_zstd_level,
                       DEFAULT_MIGRATE_MULTIFD_ZSTD_LEVEL),
+#ifdef CONFIG_LINUX
+    DEFINE_PROP_BOOL("zero_copy_send", MigrationState,
+                      parameters.zero_copy_send, false),
+#endif
     DEFINE_PROP_SIZE("xbzrle-cache-size", MigrationState,
                       parameters.xbzrle_cache_size,
                       DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE),
@@ -4303,6 +4332,9 @@ static void migration_instance_init(Object *obj)
     params->has_multifd_compression = true;
     params->has_multifd_zlib_level = true;
     params->has_multifd_zstd_level = true;
+#ifdef CONFIG_LINUX
+    params->has_zero_copy_send = true;
+#endif
     params->has_xbzrle_cache_size = true;
     params->has_max_postcopy_bandwidth = true;
     params->has_max_cpu_throttle = true;
diff --git a/migration/migration.h b/migration/migration.h
index a863032b71..e8f2941a55 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -375,6 +375,11 @@ MultiFDCompression migrate_multifd_compression(void);
 int migrate_multifd_zlib_level(void);
 int migrate_multifd_zstd_level(void);
 
+#ifdef CONFIG_LINUX
+bool migrate_use_zero_copy_send(void);
+#else
+#define migrate_use_zero_copy_send() (false)
+#endif
 int migrate_use_xbzrle(void);
 uint64_t migrate_xbzrle_cache_size(void);
 bool migrate_colo_enabled(void);
diff --git a/migration/socket.c b/migration/socket.c
index 05705a32d8..3754d8f72c 100644
--- a/migration/socket.c
+++ b/migration/socket.c
@@ -74,9 +74,16 @@ static void socket_outgoing_migration(QIOTask *task,
 
     if (qio_task_propagate_error(task, &err)) {
         trace_migration_socket_outgoing_error(error_get_pretty(err));
-    } else {
-        trace_migration_socket_outgoing_connected(data->hostname);
+           goto out;
     }
+
+    trace_migration_socket_outgoing_connected(data->hostname);
+
+    if (migrate_use_zero_copy_send()) {
+        error_setg(&err, "Zero copy send not available in migration");
+    }
+
+out:
     migration_channel_connect(data->s, sioc, data->hostname, err);
     object_unref(OBJECT(sioc));
 }
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index 93061a11af..622c783c32 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -1309,6 +1309,12 @@ 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;
+#ifdef CONFIG_LINUX
+    case MIGRATION_PARAMETER_ZERO_COPY_SEND:
+        p->has_zero_copy_send = true;
+        visit_type_bool(v, param, &p->zero_copy_send, &err);
+        break;
+#endif
     case MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE:
         p->has_xbzrle_cache_size = true;
         if (!visit_type_size(v, param, &cache_size, &err)) {
diff --git a/qapi/migration.json b/qapi/migration.json
index 409eb086a2..2222f44250 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -741,6 +741,13 @@
 #                      will consume more CPU.
 #                      Defaults to 1. (Since 5.0)
 #
+# @zero-copy-send: Controls behavior on sending memory pages on migration.
+#                  When true, enables a zero-copy mechanism for sending
+#                  memory pages, if host supports it.
+#                  Requires that QEMU be permitted to use locked memory
+#                  for guest RAM pages.
+#                  Defaults to false. (Since 7.1)
+#
 # @block-bitmap-mapping: Maps block nodes and bitmaps on them to
 #                        aliases for the purpose of dirty bitmap migration.  Such
 #                        aliases may for example be the corresponding names on the
@@ -780,6 +787,7 @@
            'xbzrle-cache-size', 'max-postcopy-bandwidth',
            'max-cpu-throttle', 'multifd-compression',
            'multifd-zlib-level' ,'multifd-zstd-level',
+           { 'name': 'zero-copy-send', 'if' : 'CONFIG_LINUX'},
            'block-bitmap-mapping' ] }
 
 ##
@@ -906,6 +914,13 @@
 #                      will consume more CPU.
 #                      Defaults to 1. (Since 5.0)
 #
+# @zero-copy-send: Controls behavior on sending memory pages on migration.
+#                  When true, enables a zero-copy mechanism for sending
+#                  memory pages, if host supports it.
+#                  Requires that QEMU be permitted to use locked memory
+#                  for guest RAM pages.
+#                  Defaults to false. (Since 7.1)
+#
 # @block-bitmap-mapping: Maps block nodes and bitmaps on them to
 #                        aliases for the purpose of dirty bitmap migration.  Such
 #                        aliases may for example be the corresponding names on the
@@ -960,6 +975,7 @@
             '*multifd-compression': 'MultiFDCompression',
             '*multifd-zlib-level': 'uint8',
             '*multifd-zstd-level': 'uint8',
+            '*zero-copy-send': { 'type': 'bool', 'if': 'CONFIG_LINUX' },
             '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
 
 ##
@@ -1106,6 +1122,13 @@
 #                      will consume more CPU.
 #                      Defaults to 1. (Since 5.0)
 #
+# @zero-copy-send: Controls behavior on sending memory pages on migration.
+#                  When true, enables a zero-copy mechanism for sending
+#                  memory pages, if host supports it.
+#                  Requires that QEMU be permitted to use locked memory
+#                  for guest RAM pages.
+#                  Defaults to false. (Since 7.1)
+#
 # @block-bitmap-mapping: Maps block nodes and bitmaps on them to
 #                        aliases for the purpose of dirty bitmap migration.  Such
 #                        aliases may for example be the corresponding names on the
@@ -1158,6 +1181,7 @@
             '*multifd-compression': 'MultiFDCompression',
             '*multifd-zlib-level': 'uint8',
             '*multifd-zstd-level': 'uint8',
+            '*zero-copy-send': { 'type': 'bool', 'if': 'CONFIG_LINUX' },
             '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
 
 ##
-- 
2.36.0