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

I'm not familiar with CPU model expansion, but here goes anyway. Eduardo Habkost <ehabkost(a)redhat.com&gt; writes: > 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 s/being/between/ > model (full) won't be safe (static), (because they would include s/they/it/

> 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. This patch does that exactly for s390x. The next patch looks like it does something for x86. What about other targets? I recommend to have this commit message explain briefly what this patch does, what later patches in this series do, and what's left for later (if anything).

> 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; > }