Re: [PATCH v4 1/2] Introduce (x86) CPU model deprecation API

[Eduardo Habkost]

On Tue, Sep 22, 2020 at 03:14:14PM +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.
> 
> Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
> ---
> Changelog
> v4:
> Move deprecation_note from X86CPUModel to X86CPUDefinition, to make it
> simple. Also, simplify 2 fields (deprecation_note and deprecated) into 1
> (deprecation_note).
> 
> v3:
> Make the deprecation implementation CPUClass generic.
> 
> 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.
> 
> ---
>  hw/core/machine.c        | 12 ++++++++++--
>  include/hw/core/cpu.h    |  3 +++
>  qapi/machine-target.json |  7 ++++++-
>  target/i386/cpu.c        |  8 ++++++++
>  4 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index ea26d61..67fff0b 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -1095,6 +1095,8 @@ 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);

machine->cpu_type can be NULL...

> +    CPUClass *cc;
>  
>      if (machine->ram_memdev_id) {
>          Object *o;
> @@ -1114,11 +1116,10 @@ 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.
> @@ -1141,6 +1142,13 @@ void machine_run_board_init(MachineState *machine)
>          }
>      }
>  
> +    /* Check if CPU type is deprecated and warn if so */
> +    cc = CPU_CLASS(oc);
> +    if (cc->deprecation_note) {

...so this will crash.

I've changed this to "if (cc && cc->deprecation_note)".

> +        warn_report("CPU model %s is deprecated -- %s", machine->cpu_type,
> +                    cc->deprecation_note);
> +    }
> +
>      machine_class->init(machine);
>  }
>  
> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index 99dc33f..c40c29d 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -155,6 +155,8 @@ struct TranslationBlock;
>   * @disas_set_info: Setup architecture specific components of disassembly 
> info
>   * @adjust_watchpoint_address: Perform a target-specific adjustment to an
>   * address before attempting to match it against watchpoints.
> + * @deprecation_note: If this CPUClass is deprecated, this field provides
> + *                    related information.
>   *
>   * Represents a CPU family or model.
>   */
> @@ -221,6 +223,7 @@ struct CPUClass {
>      vaddr (*adjust_watchpoint_address)(CPUState *cpu, vaddr addr, int len);
>      void (*tcg_initialize)(void);
>  
> +    const char *deprecation_note;
>      /* Keep non-pointer data at the end to minimize holes.  */
>      int gdb_num_core_regs;
>      bool gdb_stop_before_watchpoint;
> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
> index 698850c..fec3bb8 100644
> --- a/qapi/machine-target.json
> +++ b/qapi/machine-target.json
> @@ -286,6 +286,10 @@
>  #            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 5.2)
> +#
>  # @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
> @@ -310,7 +314,8 @@
>              '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 1c58f76..323c7e3 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -1633,6 +1633,7 @@ typedef struct X86CPUDefinition {
>       * If NULL, version 1 will be registered automatically.
>       */
>      const X86CPUVersionDefinition *versions;
> +    const char *deprecation_note;
>  } X86CPUDefinition;
>  
>  /* Reference to a specific CPU model version */
> @@ -4992,6 +4993,11 @@ 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;
> +    if (cc->model && cc->model->cpudef->deprecation_note) {
> +        info->deprecated = true;
> +    } else {
> +        info->deprecated = false;
> +    }
>      /*
>       * Old machine types won't report aliases, so that alias translation
>       * doesn't break compatibility with previous QEMU versions.
> @@ -5382,9 +5388,11 @@ static void x86_cpu_cpudef_class_init(ObjectClass *oc, 
> void *data)
>  {
>      X86CPUModel *model = data;
>      X86CPUClass *xcc = X86_CPU_CLASS(oc);
> +    CPUClass *cc = CPU_CLASS(oc);
>  
>      xcc->model = model;
>      xcc->migration_safe = true;
> +    cc->deprecation_note = model->cpudef->deprecation_note;
>  }
>  
>  static void x86_register_cpu_model_type(const char *name, X86CPUModel *model)
> -- 
> 1.8.3.1
> 
> 

-- 
Eduardo