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Re: [PATCH v2 1/2] Introduce (x86) CPU model deprecation API
From: |
Robert Hoo |
Subject: |
Re: [PATCH v2 1/2] Introduce (x86) CPU model deprecation API |
Date: |
Fri, 11 Sep 2020 14:22:51 +0800 |
On Wed, 2020-09-09 at 14:15 -0400, 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.
>
> 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.
>
Because the Warning message composing is target-specific, using
X86CPUVersionDefinition.note.
Other targets can have their own warning message composing approaches.
> > +
> > 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".
Sure.
>
> > +#
> > # @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?
Just kind of compulsion of avoiding unnecessary if() :-). 'v' can only
be one of CPU_VERSION_AUTO and CPU_VERSION_LATEST, unnecessary to judge
twice.
>
> > 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.
Because it is unused by other features, I use it to store model
specific deprecation message.
>
> > + 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()?
>
All these are to fulfill the target you expected earlier:
"We need a proper CPU model deprecation API. Deprecation info
should appear on query-cpu-definitions and should trigger a
warning when using the CPU model."
So I think each deprecated model shall have its own deprecation
message, e.g. by which version it's going to be deprecation, etc.
> > +}
> > +
> > 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
> >
>
>