Re: [PATCH v2 1/2] Introduce (x86) CPU model deprecation API

[Philippe Mathieu-Daudé]

On 9/9/20 8:15 PM, Eduardo Habkost wrote:
> Hi,
> 
> Thanks for the patch, and sorry for taking so long to review
> this.  I'm finally getting to the patches that were postponed to
> 5.2.

Sorry I missed that patch too.

Why restrict this to CPUClass, and not provide this feature to
all ObjectClass?

> 
> Comments and questions below:
> 
> On Thu, Jun 11, 2020 at 10:47:55AM +0800, Robert Hoo wrote:
>> Complement versioned CPU model framework with the ability of marking some
>> versions deprecated. When that CPU model is chosen, get some warning. The
>> warning message is customized, e.g. telling in which future QEMU version will
>> it be obsoleted.
>> The deprecation message will also appear by x86_cpu_list_entry(), e.g. '-cpu
>> help'.
>> QMP 'query-cpu-definitions' will also return a bool value indicating the
>> deprecation status.
>>
>> Changes in v2:
>> Move deprecation check from parse_cpu_option() to machine_run_board_init(), 
>> so
>> that it can cover implicit cpu_type assignment cases.
>> Add qapi new member documentation. Thanks Eric for comment and guidance on 
>> qapi.
>>
>> Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
>> ---
>>  hw/core/machine.c        | 11 +++++++++--
>>  include/hw/core/cpu.h    |  1 +
>>  qapi/machine-target.json |  7 ++++++-
>>  target/i386/cpu.c        | 45 +++++++++++++++++++++++++++++++++++++++++++--
>>  4 files changed, 59 insertions(+), 5 deletions(-)
>>
>> diff --git a/hw/core/machine.c b/hw/core/machine.c
>> index bb3a7b1..9318964 100644
>> --- a/hw/core/machine.c
>> +++ b/hw/core/machine.c
>> @@ -1083,6 +1083,8 @@ MemoryRegion *machine_consume_memdev(MachineState 
>> *machine,
>>  void machine_run_board_init(MachineState *machine)
>>  {
>>      MachineClass *machine_class = MACHINE_GET_CLASS(machine);
>> +    ObjectClass *oc = object_class_by_name(machine->cpu_type);
>> +    CPUClass *cc;
>>  
>>      if (machine->ram_memdev_id) {
>>          Object *o;
>> @@ -1102,11 +1104,10 @@ void machine_run_board_init(MachineState *machine)
>>       * specified a CPU with -cpu check here that the user CPU is supported.
>>       */
>>      if (machine_class->valid_cpu_types && machine->cpu_type) {
>> -        ObjectClass *class = object_class_by_name(machine->cpu_type);
>>          int i;
>>  
>>          for (i = 0; machine_class->valid_cpu_types[i]; i++) {
>> -            if (object_class_dynamic_cast(class,
>> +            if (object_class_dynamic_cast(oc,
>>                                            
>> machine_class->valid_cpu_types[i])) {
>>                  /* The user specificed CPU is in the valid field, we are
>>                   * good to go.
>> @@ -1129,6 +1130,12 @@ void machine_run_board_init(MachineState *machine)
>>          }
>>      }
>>  
>> +    /* Check if CPU type is deprecated and warn if so */
>> +    cc = CPU_CLASS(oc);
>> +    if (cc->deprecation_check) {
>> +        cc->deprecation_check(oc);
>> +    }
> 
> Why do we need target-specific code here?  A CPUClass::deprecated
> field would be much simpler.
> 
>> +
>>      machine_class->init(machine);
>>  }
>>  
>> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
>> index 497600c..1ca47dc 100644
>> --- a/include/hw/core/cpu.h
>> +++ b/include/hw/core/cpu.h
>> @@ -218,6 +218,7 @@ typedef struct CPUClass {
>>      void (*disas_set_info)(CPUState *cpu, disassemble_info *info);
>>      vaddr (*adjust_watchpoint_address)(CPUState *cpu, vaddr addr, int len);
>>      void (*tcg_initialize)(void);
>> +    void (*deprecation_check)(ObjectClass *oc);
>>  
>>      /* Keep non-pointer data at the end to minimize holes.  */
>>      int gdb_num_core_regs;
>> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
>> index f2c8294..c24f506 100644
>> --- a/qapi/machine-target.json
>> +++ b/qapi/machine-target.json
>> @@ -285,6 +285,10 @@
>>  #            in the VM configuration, because aliases may stop being
>>  #            migration-safe in the future (since 4.1)
>>  #
>> +# @deprecated: If true, this CPU model is deprecated and may be removed in
>> +#              in some future version of QEMU according to the QEMU 
>> deprecation
>> +#              policy. (since 5.1)
> 
> Next version needs to say "since 5.2".
> 
>> +#
>>  # @unavailable-features is a list of QOM property names that
>>  # represent CPU model attributes that prevent the CPU from running.
>>  # If the QOM property is read-only, that means there's no known
>> @@ -309,7 +313,8 @@
>>              'static': 'bool',
>>              '*unavailable-features': [ 'str' ],
>>              'typename': 'str',
>> -            '*alias-of' : 'str' },
>> +            '*alias-of' : 'str',
>> +            'deprecated' : 'bool' },
>>    'if': 'defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_I386) 
>> || defined(TARGET_S390X) || defined(TARGET_MIPS)' }
>>  
>>  ##
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index ba05da3..0d8638a 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -1599,6 +1599,7 @@ typedef struct X86CPUVersionDefinition {
>>      const char *alias;
>>      const char *note;
>>      PropValue *props;
>> +    bool       deprecated;
>>  } X86CPUVersionDefinition;
>>  
>>  /* Base definition for a CPU model */
>> @@ -1638,6 +1639,11 @@ struct X86CPUModel {
>>       * This matters only for "-cpu help" and query-cpu-definitions
>>       */
>>      bool is_alias;
>> +    /*
>> +     * If true, this model is deprecated, and may be removed in the future.
>> +     * Trying to use it now will cause a warning.
>> +     */
>> +    bool deprecated;
>>  };
>>  
>>  /* Get full model name for CPU version */
>> @@ -4128,8 +4134,7 @@ static X86CPUVersion 
>> x86_cpu_model_resolve_version(const X86CPUModel *model)
>>      X86CPUVersion v = model->version;
>>      if (v == CPU_VERSION_AUTO) {
>>          v = default_cpu_version;
>> -    }
>> -    if (v == CPU_VERSION_LATEST) {
>> +    } else if (v == CPU_VERSION_LATEST) {
> 
> Why is this change necessary?
> 
>>          return x86_cpu_model_last_version(model);
>>      }
>>      return v;
>> @@ -4975,6 +4980,7 @@ static void x86_cpu_definition_entry(gpointer data, 
>> gpointer user_data)
>>      info->migration_safe = cc->migration_safe;
>>      info->has_migration_safe = true;
>>      info->q_static = cc->static_model;
>> +    info->deprecated = cc->model ? cc->model->deprecated : false;
>>      /*
>>       * Old machine types won't report aliases, so that alias translation
>>       * doesn't break compatibility with previous QEMU versions.
>> @@ -5411,6 +5417,7 @@ static void x86_register_cpudef_types(X86CPUDefinition 
>> *def)
>>          m->cpudef = def;
>>          m->version = vdef->version;
>>          m->note = vdef->note;
>> +        m->deprecated = vdef->deprecated;
>>          x86_register_cpu_model_type(name, m);
>>  
>>          if (vdef->alias) {
>> @@ -5418,6 +5425,8 @@ static void x86_register_cpudef_types(X86CPUDefinition 
>> *def)
>>              am->cpudef = def;
>>              am->version = vdef->version;
>>              am->is_alias = true;
>> +            am->note = vdef->note;
> 
> Is this extra line related to the deprecation feature?
> 
> It doesn't seem related, and it doesn't seem necessary as the
> `note` field is already ignored for alias CPU models.
> 
>> +            am->deprecated = vdef->deprecated;
>>              x86_register_cpu_model_type(vdef->alias, am);
>>          }
>>      }
>> @@ -7233,6 +7242,37 @@ static Property x86_cpu_properties[] = {
>>      DEFINE_PROP_END_OF_LIST()
>>  };
>>  
>> +static void x86_cpu_deprecation_check(ObjectClass *oc)
>> +{
>> +    X86CPUClass *xcc = X86_CPU_CLASS(oc);
>> +    X86CPUVersion effective_version;
>> +    const X86CPUVersionDefinition *vdef;
>> +
>> +    if (xcc->model == NULL) {
>> +        return;
>> +    }
>> +
>> +    if (xcc->model->version == CPU_VERSION_LEGACY) {
>> +        /* Treat legacy version as v1 */
>> +        effective_version = 1;
>> +    } else {
>> +        effective_version = x86_cpu_model_resolve_version(xcc->model);
>> +    }
>> +
>> +    vdef = xcc->model->cpudef->versions;
>> +
>> +    if (vdef == NULL) {
>> +        return;
>> +    } else {
>> +        if (vdef[effective_version - 1].deprecated) {
>> +            warn_report("Effective CPU model '%s' -- %s",
>> +                    x86_cpu_versioned_model_name(xcc->model->cpudef,\
>> +                                                effective_version),
>> +                    vdef[effective_version - 1].note);
>> +        }
>> +    }
> 
> Why do we need this extra logic?  Isn't it simpler to just add a
> bool CPUClass::deprecated field, and set:
> 
>    cpu->deprecated = model->deprecated;
> 
> inside x86_cpu_cpudef_class_init()?
> 
>> +}
>> +
>>  static void x86_cpu_common_class_init(ObjectClass *oc, void *data)
>>  {
>>      X86CPUClass *xcc = X86_CPU_CLASS(oc);
>> @@ -7291,6 +7331,7 @@ static void x86_cpu_common_class_init(ObjectClass *oc, 
>> void *data)
>>      cc->tlb_fill = x86_cpu_tlb_fill;
>>  #endif
>>      cc->disas_set_info = x86_disas_set_info;
>> +    cc->deprecation_check = x86_cpu_deprecation_check;
>>  
>>      dc->user_creatable = true;
>>  }
>> -- 
>> 1.8.3.1
>>
>