Re: [Qemu-devel] [PATCH for-2.9 17/17] target-i386: Implement query-cpu-model-expansion QMP command

[Markus Armbruster <armbru@redhat.com>]

Eduardo Habkost <ehabkost@redhat.com> writes:

> Implement query-cpu-model-expansion for target-i386.
>
> The code needs to be careful to handle non-migration-safe
> features ("pmu" and "host-cache-info") according to the expansion
> type.
>
> Cc: libvir-list@redhat.com
> Cc: Jiri Denemark <jdenemar@redhat.com>
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
>  tests/Makefile.include |   3 +
>  monitor.c              |   4 +-
>  target-i386/cpu.c      | 195 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 200 insertions(+), 2 deletions(-)
>
> diff --git a/tests/Makefile.include b/tests/Makefile.include
> index 63c4347..c7bbfca 100644
> --- a/tests/Makefile.include
> +++ b/tests/Makefile.include
> @@ -251,6 +251,9 @@ check-qtest-x86_64-y += $(check-qtest-i386-y)
>  gcov-files-i386-y += i386-softmmu/hw/timer/mc146818rtc.c
>  gcov-files-x86_64-y = $(subst i386-softmmu/,x86_64-softmmu/,$(gcov-files-i386-y))
>  
> +check-simpleqtest-x86_64-y += $(SRC_PATH)/tests/query-cpu-model-test.py
> +check-simpleqtest-i386-y += $(SRC_PATH)/tests/query-cpu-model-test.py
> +
>  check-qtest-alpha-y = tests/boot-serial-test$(EXESUF)
>  
>  check-qtest-mips-y = tests/endianness-test$(EXESUF)
> diff --git a/monitor.c b/monitor.c
> index 0841d43..90c12b3 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -983,8 +983,10 @@ static void qmp_unregister_commands_hack(void)
>  #ifndef TARGET_ARM
>      qmp_unregister_command("query-gic-capabilities");
>  #endif
> -#if !defined(TARGET_S390X)
> +#if !defined(TARGET_S390X) && !defined(TARGET_I386)
>      qmp_unregister_command("query-cpu-model-expansion");
> +#endif
> +#if !defined(TARGET_S390X)
>      qmp_unregister_command("query-cpu-model-baseline");
>      qmp_unregister_command("query-cpu-model-comparison");
>  #endif
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index bf4ac09..198014a 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -29,10 +29,14 @@
>  #include "qemu/option.h"
>  #include "qemu/config-file.h"
>  #include "qapi/qmp/qerror.h"
> +#include "qapi/qmp/qstring.h"
> +#include "qapi/qmp/qdict.h"
> +#include "qapi/qmp/qbool.h"
>  
>  #include "qapi-types.h"
>  #include "qapi-visit.h"
>  #include "qapi/visitor.h"
> +#include "qom/qom-qobject.h"
>  #include "sysemu/arch_init.h"
>  
>  #if defined(CONFIG_KVM)
> @@ -2259,7 +2263,7 @@ static void x86_cpu_apply_props(X86CPU *cpu, PropValue *props)
>      }
>  }
>  
> -/* Load data from X86CPUDefinition
> +/* Load data from X86CPUDefinition into a X86CPU object
>   */
>  static void x86_cpu_load_def(X86CPU *cpu, X86CPUDefinition *def, Error **errp)
>  {
> @@ -2268,6 +2272,11 @@ static void x86_cpu_load_def(X86CPU *cpu, X86CPUDefinition *def, Error **errp)
>      char host_vendor[CPUID_VENDOR_SZ + 1];
>      FeatureWord w;
>  
> +    /*NOTE: any property set by this function should be returned by

Space between /* and comment text, please.

Also, consider adding wings to both ends of multi-line comments.

> +     * x86_cpu_to_dict(), so CPU model data returned by
> +     * query-cpu-model-expansion is always complete.
> +     */
> +
>      /* CPU models only set _minimum_ values for level/xlevel: */
>      object_property_set_int(OBJECT(cpu), def->level, "min-level", errp);
>      object_property_set_int(OBJECT(cpu), def->xlevel, "min-xlevel", errp);
> @@ -2312,6 +2321,190 @@ static void x86_cpu_load_def(X86CPU *cpu, X86CPUDefinition *def, Error **errp)
>  
>  }
>  
> +/* Convert CPU model data from X86CPU object to a property dictionary
> + * that can recreate exactly the same CPU model.
> + *
> + * This function does the opposite of x86_cpu_load_def(). Any
> + * property changed by x86_cpu_load_def() or instance_init
> + * methods should be returned by this function too.
> + */
> +static void x86_cpu_to_dict(X86CPU *cpu, QDict *props, Error **errp)
> +{
> +    Object *obj = OBJECT(cpu);
> +    FeatureWord w;
> +    PropValue *pv;
> +
> +    /* This code could simply iterate over all writeable properties in the
> +     * CPU object, and return all of them. But then the aliases properties

"alias properties"?

> +     * would be returned as well. Returning only the known features
> +     * is more reliable.
> +     */
> +    qdict_put_obj(props, "min-level",
> +                  object_property_get_qobject(obj, "min-level", errp));
> +    qdict_put_obj(props, "min-xlevel",
> +                  object_property_get_qobject(obj, "min-xlevel", errp));
> +
> +    qdict_put_obj(props, "family",
> +                  object_property_get_qobject(obj, "family", errp));
> +    qdict_put_obj(props, "model",
> +                  object_property_get_qobject(obj, "model", errp));
> +    qdict_put_obj(props, "stepping",
> +                  object_property_get_qobject(obj, "stepping", errp));
> +    qdict_put_obj(props, "model-id",
> +                  object_property_get_qobject(obj, "model-id", errp));

Incorrect use of the error API: if more than one call fails, the second
failure will trip the assertion in error_setv().

If errors should not happen here, use &error_abort.

If errors need to be handled, see "Receive and accumulate multiple
errors" in error.h.

Consider "more than four, use a for":

       static char *prop_name[] = {
           "min-level", "min-xlevel", "family", "model", "stepping",
           "model-id", NULL
       };

       for (pname = prop_name; *pname, pname++) {
           qdict_put_obj(props, *pname,
                         object_property_get_qobject(obj, *pname,
                                                     &error_abort));
       }

> +
> +    for (w = 0; w < FEATURE_WORDS; w++) {
> +        FeatureWordInfo *fi = &feature_word_info[w];
> +        int bit;
> +        for (bit = 0; bit < 32; bit++) {
> +            if (!fi->feat_names[bit]) {
> +                continue;
> +            }
> +            qdict_put_obj(props, fi->feat_names[bit],
> +                          object_property_get_qobject(obj, fi->feat_names[bit],
> +                                                      errp));
> +        }
> +    }
> +
> +    for (pv = kvm_default_props; pv->prop; pv++) {
> +        qdict_put_obj(props, pv->prop,
> +                      object_property_get_qobject(obj, pv->prop, errp));
> +    }
> +    for (pv = tcg_default_props; pv->prop; pv++) {
> +        qdict_put_obj(props, pv->prop,
> +                      object_property_get_qobject(obj, pv->prop, errp));
> +    }
> +
> +    qdict_put_obj(props, "vendor",
> +                  object_property_get_qobject(obj, "vendor", errp));
> +
> +    /* Set by "host": */
> +    qdict_put_obj(props, "lmce",
> +                  object_property_get_qobject(obj, "lmce", errp));
> +    qdict_put_obj(props, "pmu",
> +                  object_property_get_qobject(obj, "pmu", errp));
> +
> +
> +    /* Other properties configurable by the user: */
> +    qdict_put_obj(props, "host-cache-info",
> +                  object_property_get_qobject(obj, "host-cache-info", errp));
> +}
> +
> +static void object_apply_props(Object *obj, QDict *props, Error **errp)
> +{
> +    const QDictEntry *prop;
> +    Error *err = NULL;
> +
> +    for (prop = qdict_first(props); prop; prop = qdict_next(props, prop)) {
> +        object_property_set_qobject(obj, qdict_entry_value(prop),
> +                                         qdict_entry_key(prop), &err);
> +        if (err) {
> +            break;
> +        }
> +    }
> +
> +    error_propagate(errp, err);
> +}
> +
> +static X86CPU *x86_cpu_from_model(CpuModelInfo *model, Error **errp)
> +{
> +    X86CPU *xc = NULL;
> +    X86CPUClass *xcc;
> +    Error *err = NULL;
> +
> +    xcc = X86_CPU_CLASS(cpu_class_by_name(TYPE_X86_CPU, model->name));
> +    if (xcc == NULL) {
> +        error_setg(&err, "CPU model '%s' not found", model->name);
> +        goto out;
> +    }
> +
> +    xc = X86_CPU(object_new(object_class_get_name(OBJECT_CLASS(xcc))));
> +    if (model->has_props) {
> +        QDict *d = qobject_to_qdict(model->props);
> +        if (!d) {
> +            error_setg(&err, "model.props must be a dictionary");
> +            goto out;

How can this happen?

> +        }
> +        object_apply_props(OBJECT(xc), d, &err);
> +        if (err) {
> +            goto out;
> +        }
> +    }
> +
> +    x86_cpu_expand_features(xc, &err);
> +    if (err) {
> +        goto out;
> +    }
> +
> +out:
> +    if (err) {
> +        error_propagate(errp, err);
> +        object_unref(OBJECT(xc));
> +        xc = NULL;
> +    }
> +    return xc;
> +}
> +
> +CpuModelExpansionInfo *arch_query_cpu_model_expansion(CpuModelExpansionType type,
> +                                                      CpuModelInfo *model,
> +                                                      Error **errp)
> +{
> +    X86CPU *xc = NULL;
> +    Error *err = NULL;
> +    CpuModelExpansionInfo *ret = g_new0(CpuModelExpansionInfo, 1);
> +    QDict *props;
> +
> +    xc = x86_cpu_from_model(model, &err);
> +    if (err) {
> +        goto out;
> +    }
> +
> +    /* We currently always do full expansion */

This comment made me go "wait, we do full expansion even when @type is
CPU_MODEL_EXPANSION_TYPE_STATIC?"  Looks like we first to full
expansion, then correct the result according to type.

> +    ret->model = g_new0(CpuModelInfo, 1);
> +    ret->model->name = g_strdup("base"); /* the only static model */
> +    props = qdict_new();
> +    ret->model->props = QOBJECT(props);
> +    ret->model->has_props = true;
> +    x86_cpu_to_dict(xc, props, &err);
> +
> +    /* Some features (pmu, host-cache-info) are not migration-safe,
> +     * and are handled differently depending on expansion type:
> +     */
> +    if (type ==  CPU_MODEL_EXPANSION_TYPE_STATIC) {

Single space after ==, please.

> +        /* static expansion force migration-unsafe features off: */
> +        ret->q_static = ret->migration_safe = true;
> +        qdict_del(props, "pmu");
> +        qdict_del(props, "host-cache-info");
> +    } else if (type == CPU_MODEL_EXPANSION_TYPE_FULL) {
> +        QObject *o;
> +        /* full expansion clear the static/migration-safe flags
> +         * to indicate migration-unsafe features are on:
> +         */
> +        ret->q_static = true;
> +        ret->migration_safe = true;
> +
> +        o = qdict_get(props, "pmu");
> +        if (o && qbool_get_bool(qobject_to_qbool(o))) {
> +            ret->q_static = ret->migration_safe = false;
> +        }
> +        o = qdict_get(props, "host-cache-info");
> +        if (o && qbool_get_bool(qobject_to_qbool(o))) {
> +            ret->q_static = ret->migration_safe = false;
> +        }
> +    } else {
> +        error_setg(&err, "The requested expansion type is not supported.");

How can this happen?

If it can, it bombs when x86_cpu_to_dict() already set an error (see
"use of the error API" above).

> +    }
> +
> +out:
> +    object_unref(OBJECT(xc));
> +    if (err) {
> +        error_propagate(errp, err);
> +        qapi_free_CpuModelExpansionInfo(ret);
> +        ret = NULL;
> +    }
> +    return ret;
> +}
> +
>  X86CPU *cpu_x86_init(const char *cpu_model)
>  {
>      return X86_CPU(cpu_generic_init(TYPE_X86_CPU, cpu_model));