[PATCH v7 3/5] migration: Add zero-copy parameter for QMP/HMP for Linux

[Leonardo Bras <leobras@redhat.com>]

Add property that allows zero-copy migration of memory pages,
and also includes a helper function migrate_use_zero_copy() 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>
---
 qapi/migration.json   | 24 ++++++++++++++++++++++++
 migration/migration.h |  5 +++++
 migration/migration.c | 32 ++++++++++++++++++++++++++++++++
 migration/socket.c    |  5 +++++
 monitor/hmp-cmds.c    |  6 ++++++
 5 files changed, 72 insertions(+)

diff --git a/qapi/migration.json b/qapi/migration.json
index bbfd48cf0b..2e62ea6ebd 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -730,6 +730,13 @@
 #                      will consume more CPU.
 #                      Defaults to 1. (Since 5.0)
 #
+# @zero-copy: 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 7.0)
+#
 # @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
@@ -769,6 +776,7 @@
            'xbzrle-cache-size', 'max-postcopy-bandwidth',
            'max-cpu-throttle', 'multifd-compression',
            'multifd-zlib-level' ,'multifd-zstd-level',
+           { 'name': 'zero-copy', 'if' : 'CONFIG_LINUX'},
            'block-bitmap-mapping' ] }
 
 ##
@@ -895,6 +903,13 @@
 #                      will consume more CPU.
 #                      Defaults to 1. (Since 5.0)
 #
+# @zero-copy: 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 7.0)
+#
 # @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
@@ -949,6 +964,7 @@
             '*multifd-compression': 'MultiFDCompression',
             '*multifd-zlib-level': 'uint8',
             '*multifd-zstd-level': 'uint8',
+            '*zero-copy': { 'type': 'bool', 'if': 'CONFIG_LINUX' },
             '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
 
 ##
@@ -1095,6 +1111,13 @@
 #                      will consume more CPU.
 #                      Defaults to 1. (Since 5.0)
 #
+# @zero-copy: 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 7.0)
+#
 # @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
@@ -1147,6 +1170,7 @@
             '*multifd-compression': 'MultiFDCompression',
             '*multifd-zlib-level': 'uint8',
             '*multifd-zstd-level': 'uint8',
+            '*zero-copy': { 'type': 'bool', 'if': 'CONFIG_LINUX' },
             '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } }
 
 ##
diff --git a/migration/migration.h b/migration/migration.h
index 8130b703eb..1489eeb165 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -339,6 +339,11 @@ 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(void);
+#else
+#define migrate_use_zero_copy() (false)
+#endif
 int migrate_use_xbzrle(void);
 uint64_t migrate_xbzrle_cache_size(void);
 bool migrate_colo_enabled(void);
diff --git a/migration/migration.c b/migration/migration.c
index 0652165610..aa8f1dc835 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -893,6 +893,10 @@ 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 = true;
+    params->zero_copy = s->parameters.zero_copy;
+#endif
     params->has_xbzrle_cache_size = true;
     params->xbzrle_cache_size = s->parameters.xbzrle_cache_size;
     params->has_max_postcopy_bandwidth = true;
@@ -1546,6 +1550,11 @@ 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) {
+        dest->zero_copy = params->zero_copy;
+    }
+#endif
     if (params->has_xbzrle_cache_size) {
         dest->xbzrle_cache_size = params->xbzrle_cache_size;
     }
@@ -1658,6 +1667,11 @@ 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) {
+        s->parameters.zero_copy = params->zero_copy;
+    }
+#endif
     if (params->has_xbzrle_cache_size) {
         s->parameters.xbzrle_cache_size = params->xbzrle_cache_size;
         xbzrle_cache_resize(params->xbzrle_cache_size, errp);
@@ -2548,6 +2562,17 @@ int migrate_multifd_zstd_level(void)
     return s->parameters.multifd_zstd_level;
 }
 
+#ifdef CONFIG_LINUX
+bool migrate_use_zero_copy(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.zero_copy;
+}
+#endif
+
 int migrate_use_xbzrle(void)
 {
     MigrationState *s;
@@ -4200,6 +4225,10 @@ 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", MigrationState,
+                      parameters.zero_copy, false),
+#endif
     DEFINE_PROP_SIZE("xbzrle-cache-size", MigrationState,
                       parameters.xbzrle_cache_size,
                       DEFAULT_MIGRATE_XBZRLE_CACHE_SIZE),
@@ -4297,6 +4326,9 @@ 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 = true;
+#endif
     params->has_xbzrle_cache_size = true;
     params->has_max_postcopy_bandwidth = true;
     params->has_max_cpu_throttle = true;
diff --git a/migration/socket.c b/migration/socket.c
index 05705a32d8..f7a77aafd3 100644
--- a/migration/socket.c
+++ b/migration/socket.c
@@ -77,6 +77,11 @@ static void socket_outgoing_migration(QIOTask *task,
     } else {
         trace_migration_socket_outgoing_connected(data->hostname);
     }
+
+    if (migrate_use_zero_copy()) {
+        error_setg(&err, "Zero copy not available in migration");
+    }
+
     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 2669156b28..35d47e250d 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -1297,6 +1297,12 @@ 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:
+        p->has_zero_copy = true;
+        visit_type_bool(v, param, &p->zero_copy, &err);
+        break;
+#endif
     case MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE:
         p->has_xbzrle_cache_size = true;
         if (!visit_type_size(v, param, &cache_size, &err)) {
-- 
2.34.1