Question to the QAPI schema maintainers below:
On Wed, Sep 05, 2018 at 01:47:55PM +0800, Robert Hoo wrote:
> On Fri, 2018-08-17 at 17:52 +0200, Paolo Bonzini wrote:
> > On 10/08/2018 16:06, Robert Hoo wrote:
> > > x86_cpu_get_feature_words(): limit to CPUID_FEATURE_WORD only.
> >
> > This should also grow support for MSR feature words.
> >
> > My suggestion is that you add another patch after patch 1 that expands
> > the definition of X86CPUFeatureWordInfo like this, and adjusts
> > x86_cpu_get_feature_words() to match the new C structs. Then this
> > patch can add MSR feature support somewhat easily.
> >
> > The QAPI definitions would then look like this:
> >
> > diff --git a/qapi/misc.json b/qapi/misc.json
> > index d450cfef21..eae9243976 100644
> > --- a/qapi/misc.json
> > +++ b/qapi/misc.json
> > @@ -2663,9 +2663,9 @@
> > 'data': [ 'EAX', 'EBX', 'ECX', 'EDX', 'ESP', 'EBP', 'ESI', 'EDI' ] }
> >
> > ##
> > -# @X86CPUFeatureWordInfo:
> > +# @X86CPUIDFeatureWordInfo:
> > #
> > -# Information about a X86 CPU feature word
> > +# Information about an X86 CPUID feature word
> > #
> > # @cpuid-input-eax: Input EAX value for CPUID instruction for that feature
> > word
> > #
> > @@ -2678,12 +2690,45 @@
> > #
> > # Since: 1.5
> > ##
> > -{ 'struct': 'X86CPUFeatureWordInfo',
> > +{ 'struct': 'X86CPUIDFeatureWordInfo',
> > 'data': { 'cpuid-input-eax': 'int',
> > '*cpuid-input-ecx': 'int',
> > 'cpuid-register': 'X86CPURegister32',
> > 'features': 'int' } }
> >
> > +##
> > +# @X86MSRFeatureWordInfo:
> > +#
> > +# Information about an X86 MSR feature word
> > +#
> > +# @index: Index of the model specific register
> > +#
> > +# @cpuid-feature: CPUID feature name that communicates the existance of
> > the MSR
> > +#
> > +# @features: value of output register, containing the feature bits
> > +#
> > +# Since: 3.1
> > +##
> > +{ 'struct': 'X86MSRFeatureWordInfo',
> > + 'data': { 'index': 'int',
> > + 'cpuid-feature': 'str',
> > + 'features': 'int' } }
> > +
> > +##
> > +# @X86CPUFeatureWordInfo:
> > +#
> > +# A discriminated record of X86 CPU feature words
> > +#
> > +# Since: 3.1
> > +##
> > +
> > +{ 'union': 'X86CPUFeatureWordInfo',
> > + 'base': { 'type': 'X86CPUFeatureWordType' },
> > + 'discriminator': 'type',
> > + 'data': {
> > + 'cpuid': 'X86CPUIDFeatureWordInfo',
> > + 'msr': 'X86MSRFeatureWordInfo' }}
> > +
> > ##
> > # @DummyForceArrays:
> > #
>
> [root@robert-ivt qemu]# git diff qapi/misc.json
> diff --git a/qapi/misc.json b/qapi/misc.json
> index d450cfe..7351dc2 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -2663,25 +2663,25 @@
> 'data': [ 'EAX', 'EBX', 'ECX', 'EDX', 'ESP', 'EBP', 'ESI', 'EDI' ] }
>
> ##
> -# @X86CPUFeatureWordInfo:
> +# @X86CPUIDFeatureWordInfo:
> #
> -# Information about a X86 CPU feature word
> +# Information about a X86 CPUID feature word
> #
> -# @cpuid-input-eax: Input EAX value for CPUID instruction for that
> feature word
> +# @input-eax: Input EAX value for CPUID instruction for that feature
> word
> #
> -# @cpuid-input-ecx: Input ECX value for CPUID instruction for that
> +# @input-ecx: Input ECX value for CPUID instruction for that
> # feature word
> #
> -# @cpuid-register: Output register containing the feature bits
> +# @register: Output register containing the feature bits
> #
> # @features: value of output register, containing the feature bits
> #
> # Since: 1.5
> ##
> -{ 'struct': 'X86CPUFeatureWordInfo',
> - 'data': { 'cpuid-input-eax': 'int',
> - '*cpuid-input-ecx': 'int',
> - 'cpuid-register': 'X86CPURegister32',
> +{ 'struct': 'X86CPUIDFeatureWordInfo',
> + 'data': { 'input-eax': 'int',
> + '*input-ecx': 'int',
> + 'register': 'X86CPURegister32',
> 'features': 'int' } }
>
> ##
> @@ -2694,6 +2694,50 @@
> { 'struct': 'DummyForceArrays',
> 'data': { 'unused': ['X86CPUFeatureWordInfo'] } }
>
> +##
> +# @X86MSRFeatureWordInfo:
> +#
> +# Information about an X86 MSR feature word
> +#
> +# @index: Index of the model specific register
> +#
> +# @cpuid-feature: CPUID feature name that communicates the existance of
> the MSR
> +#
> +# @features: value of output register, containing the feature bits
> +#
> +# Since: 3.1
> +##
> +{ 'struct': 'X86MSRFeatureWordInfo',
> + 'data': { 'index': 'int',
> + 'cpuid-feature': 'str',
> + 'features': 'int' } }
> +
> +##
> +# @X86CPUFeatureWordType:
> +#
> +# Kinds of X86 CPU feature words
> +#
> +# @cpuid: A CPUID leaf
> +#
> +# @msr: An MSR
> +##
> +{ 'enum': 'X86CPUFeatureWordType',
> + 'data': [ 'cpuid', 'msr' ] }
> +
> +##
> +# @X86CPUFeatureWordInfo:
> +#
> +# A discriminated record of X86 CPU feature words
> +#
> +# Since: 3.1
> +##
> +{ 'union': 'X86CPUFeatureWordInfo',
> + 'base': { 'type': 'X86CPUFeatureWordType' },
> + 'discriminator': 'type',
> + 'data': {
> + 'cpuid': 'X86CPUIDFeatureWordInfo',
> + 'msr': 'X86MSRFeatureWordInfo' }}
Question to the QAPI maintainers: is this really allowed? With
this change, data that conforms to the new schema may not conform
to the old schema, because now the "input-eax" field will become
optional.
AFAICS, this will break the existing libvirt code: it will make
qemuMonitorJSONParseCPUx86Features() error out because it won't
find the "input-eax" field on all X86CPUFeatureWordInfo elements.
> +
>
> ##
> # @NumaOptionsType:
>
> Hi Paolo,
>
> above is my draft change on the qapi json file. 1 question:
> struct X86MSRFeatureWordInfo {
> int64_t index;
> char *cpuid_feature;
> int64_t features;
> };
> how to have a "const" prefix the "char *"?
QAPI will make qapi_free_X86MSRFeatureWordInfo(i) call
g_free(i->cpuid_feature), which means you aren't supposed to use
a const char pointer here. You can use g_strdup() if necessary.
> >
> > I'm not sure if the cpuid-feature field is useful for libvirt and
> > other management applications. Eduardo, what do you think?
It looks like a very limited way to represent dependencies
between CPU features because it applies only to MSRs. I would
prefer to represent feature dependencies in a more generic way
later, and only if really necessary.
> >
> > Thanks,
> >
> > Paolo
>
>
--
Eduardo
