Re: [Qemu-devel] [PATCH v2 1/5] i386: Add support for IA32_PRED_CMD and IA32_ARCH_CAPABILITIES MSRs

[Paolo Bonzini]

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.

Thanks,

Paolo

> And, if I implemented ARCH_CAPABILITIES-bits features in FeatureWord,
> then no necessity of having it in kvm_msr_entries, right?