Re: [libvirt] [Qemu-devel] [PATCH for-2.9 14/17] qapi: add static/migration-safe info to query-cpu-model-expansion

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(a)de.ibm.com&gt; Cc: Christian Borntraeger <borntraeger(a)de.ibm.com&gt; Cc: David Hildenbrand <david(a)redhat.com&gt; Cc: libvir-list(a)redhat.com Cc: Jiri Denemark <jdenemar(a)redhat.com&gt; Cc: "Jason J. Herne" <jjherne(a)linux.vnet.ibm.com&gt; Cc: Markus Armbruster <armbru(a)redhat.com&gt; Cc: Eric Blake <eblake(a)redhat.com&gt; Signed-off-by: Eduardo Habkost <ehabkost(a)redhat.com&gt; --- 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; }