Re: [PATCH RFC 09/22] i386: add reserved FEAT_HYPERV_ECX CPUID leaf

[Vitaly Kuznetsov]

Eduardo Habkost <ehabkost@redhat.com> writes:

> On Fri, Sep 04, 2020 at 04:54:18PM +0200, Vitaly Kuznetsov wrote:
>> As a preparation to expanding Hyper-V CPU features early, add
>> reserved FEAT_HYPERV_ECX CPUID leaf.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  target/i386/cpu.c | 5 +++++
>>  target/i386/cpu.h | 1 +
>>  target/i386/kvm.c | 2 ++
>>  3 files changed, 8 insertions(+)
>> 
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index ef3c672cf415..70588571ccb1 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -974,6 +974,11 @@ static FeatureWordInfo feature_word_info[FEATURE_WORDS] 
>> = {
>>          },
>>          .cpuid = { .eax = 0x40000003, .reg = R_EBX, },
>>      },
>> +    [FEAT_HYPERV_ECX] = {
>> +        .type = CPUID_FEATURE_WORD,
>> +        /* reserved */
>
> What does "reserved" mean here?

This is actually from TLFS, these bits are currently reserved and there
are no features represented by them. We can, of course, short-circuit
this to '0' but I'd prefer to keep it for consistency. I can change to
something like 'Reserved as of TLFS v6.0b' to make it clear. 

>
>> +        .cpuid = { .eax = 0x40000003, .reg = R_ECX, },
>> +    },
>>      [FEAT_HYPERV_EDX] = {
>>          .type = CPUID_FEATURE_WORD,
>>          .feat_names = {
>> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
>> index 095d0bf75493..39e0e89aa41f 100644
>> --- a/target/i386/cpu.h
>> +++ b/target/i386/cpu.h
>> @@ -521,6 +521,7 @@ typedef enum FeatureWord {
>>      FEAT_KVM_HINTS,     /* CPUID[4000_0001].EDX */
>>      FEAT_HYPERV_EAX,    /* CPUID[4000_0003].EAX */
>>      FEAT_HYPERV_EBX,    /* CPUID[4000_0003].EBX */
>> +    FEAT_HYPERV_ECX,    /* CPUID[4000_0003].ECX */
>>      FEAT_HYPERV_EDX,    /* CPUID[4000_0003].EDX */
>>      FEAT_HV_RECOMM_EAX, /* CPUID[4000_0004].EAX */
>>      FEAT_HV_NESTED_EAX, /* CPUID[4000_000A].EAX */
>> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
>> index 96ac719adca1..259be2d514dd 100644
>> --- a/target/i386/kvm.c
>> +++ b/target/i386/kvm.c
>> @@ -1251,6 +1251,7 @@ static int hyperv_handle_properties(CPUState *cs,
>>          if (c) {
>>              env->features[FEAT_HYPERV_EAX] = c->eax;
>>              env->features[FEAT_HYPERV_EBX] = c->ebx;
>> +            env->features[FEAT_HYPERV_ECX] = c->ecx;
>>              env->features[FEAT_HYPERV_EDX] = c->edx;
>>          }
>>  
>> @@ -1350,6 +1351,7 @@ static int hyperv_handle_properties(CPUState *cs,
>>      c->function = HV_CPUID_FEATURES;
>>      c->eax = env->features[FEAT_HYPERV_EAX];
>>      c->ebx = env->features[FEAT_HYPERV_EBX];
>> +    c->ecx = env->features[FEAT_HYPERV_ECX];
>>      c->edx = env->features[FEAT_HYPERV_EDX];
>>  
>>      c = &cpuid_ent[cpuid_i++];
>> -- 
>> 2.25.4
>> 

-- 
Vitaly