On x86, "-cpu host" enables some features that can't be
represented by a static CPU model definition: cache info
passthrough ("host-cache-info") and PMU passthrough ("pmu"). This
means a type=static expansion of "host" can't include those
features.
A type=full expansion of "host", on the other hand, can include
those features, but then the returned data won't be a static CPU
model representation.
Add a note to the documentation explaining that when using CPU
models that include non-migration-safe features, users need to
choose being precision and safety: a precise expansion of the CPU
model (full) won't be safe (static), (because they would include
pmu=on and host-cache-info=on), and a safe (static) expansion of
the CPU model won't be precise.
Architectures where CPU model expansion is always migration-safe
(e.g. s390x) can simply do what they already do, and set
'migration-safe' and 'static' to true.
Cc: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: libvir-list@xxxxxxxxxx
Cc: Jiri Denemark <jdenemar@xxxxxxxxxx>
Cc: "Jason J. Herne" <jjherne@xxxxxxxxxxxxxxxxxx>
Cc: Markus Armbruster <armbru@xxxxxxxxxx>
Cc: Eric Blake <eblake@xxxxxxxxxx>
Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
---
qapi-schema.json | 25 ++++++++++++++++++++++++-
target-s390x/cpu_models.c | 4 ++++
2 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/qapi-schema.json b/qapi-schema.json
index 8d113f8..a102534 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -3291,6 +3291,15 @@
# migration-safe, but allows tooling to get an insight and work with
# model details.
#
+# Note: When a non-migration-safe CPU model is expanded in static mode, some
+# features enabled by the CPU model may be omitted, because they can't be
+# implemented by a static CPU model definition (e.g. cache info passthrough and
+# PMU passthrough in x86). If you need an accurate representation of the
+# features enabled by a non-migration-safe CPU model, use @full. If you need a
+# static representation that will keep ABI compatibility even when changing QEMU
+# version or machine-type, use @static (but keep in mind that some features may
+# be omitted).
+#
# Since: 2.8.0
##
{ 'enum': 'CpuModelExpansionType',
@@ -3304,10 +3313,24 @@
#
# @model: the expanded CpuModelInfo.
#
+# @migration-safe: the expanded CPU model in @model is a migration-safe
+# CPU model. See @CpuDefinitionInfo.migration-safe.
+# If expansion type was @static, this is always true.
+# (since 2.9)
+#
+# @static: the expanded CPU model in @model is a static CPU model.
+# See @CpuDefinitionInfo.static. If expansion type was @static,
+# this is always true.
+# (since 2.9)
+#
+# query-cpu-model-expansion with static expansion type should always
+# return a static and migration-safe expansion.
+#
# Since: 2.8.0
##
{ 'struct': 'CpuModelExpansionInfo',
- 'data': { 'model': 'CpuModelInfo' } }
+ 'data': { 'model': 'CpuModelInfo', 'static': 'bool',
+ 'migration-safe': 'bool' } }
##
diff --git a/target-s390x/cpu_models.c b/target-s390x/cpu_models.c
index 5b66d33..f934add 100644
--- a/target-s390x/cpu_models.c
+++ b/target-s390x/cpu_models.c
@@ -448,6 +448,10 @@ CpuModelExpansionInfo *arch_query_cpu_model_expansion(CpuModelExpansionType type
/* convert it back to a static representation */
expansion_info = g_malloc0(sizeof(*expansion_info));
expansion_info->model = g_malloc0(sizeof(*expansion_info->model));
+
+ /* We always expand to a static and migration-safe CpuModelInfo */
+ expansion_info->q_static = true;
+ expansion_info->migration_safe = true;
cpu_info_from_model(expansion_info->model, &s390_model, delta_changes);
return expansion_info;
}
--
2.7.4
--
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