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From: Robert Hoo <robert.hu@linux.intel.com>
Date: Tue, 03 Jul 2018 19:07:51 +0800
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Subject: Re: [Qemu-devel] [PATCH v2 1/5] i386: Add support for IA32_PRED_CMD
 and IA32_ARCH_CAPABILITIES MSRs
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>, qemu-devel@nongnu.org, wei.w.wang@intel.com

On Tue, 2018-07-03 at 11:06 +0200, Paolo Bonzini wrote:
> On 03/07/2018 10:48, Robert Hoo wrote:
> >>
> >> However, I suggest adding it to the FeatureWord enum, since everything
> >> that handles FeatureWord applies to this new kind of MSR as well.
> >> Currently FeatureWord is only for CPUID leaves, but it doesn't have to
> >> be like that.
> >>
> > I think this will be changing struct FeatureWordInfo, which is designed
> > for cpuid enumerations. You must not want to do that. May I know more
> > details about your thought?
> 
> The simplest way is to put CPUIDs first and MSRs second in FeatureWord.
> Then you can do
> 
>      FEAT_XSAVE_COMP_LO, /* CPUID[EAX=0xd,ECX=0].EAX */
>      FEAT_XSAVE_COMP_HI, /* CPUID[EAX=0xd,ECX=0].EDX */
> +    FEATURE_WORDS_NUM_CPUID,
> +    FEATURE_WORDS_FIRST_MSR = FEATURE_WORDS_NUM_CPUID,
> +    FEAT_MSR_ARCH_CAPABILITIES = FEATURE_WORDS_FIRST_MSR,
>      FEATURE_WORDS,
> };
> 
> #define FEATURE_WORDS_NUM_MSRS (FEATURE_WORDS - \
>                                 FEATURE_WORDS_FIRST_MSR)
> 
> Then the existing loops that use FeatureWordInfo can go up to
> FEATURE_WORDS_NUM_CPUID.

Emm... Understand your point now. It is a little risky, all references
to FEATURE_WORDS need to be updated carefully.
OK, let me try to think in this way.
Perhaps, I'll need to define a new 'struct FeautureWordMsrInfo' to
describe feature words from MSR, in parallel to current FeatureWordInfo
(or better rename it to FeatureWordCpuidInfo).
> 
> Thanks,
> 
> Paolo
> 
> > And, if I implemented ARCH_CAPABILITIES-bits features in FeatureWord,
> > then no necessity of having it in kvm_msr_entries, right?
> 
And would you help confirm with my this point?