Re: [PATCH v4 17/21] i386: support 'hv-passthrough, hv-feature=off' on the command line

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Igor Mammedov <imammedo@redhat.com> writes:

> On Wed, 10 Feb 2021 17:40:29 +0100
> Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
>> Currently, we support 'hv-passthrough,hv-feature=on' enablement, this
>> is supposed to mean "hv-feature is mandatory, don't start without it". Add
>> support for 'hv-passthrough,hv-feature=off' meaning "enable everything
>> supported by the host except for hv-feature".
>> 
>> While on it, make 'hv-passthrough' parse semantics in-line with other
>> options in qemu: when specified, it overrides what was previously set with
>> what's supported by the host. This can later be modified with 'hv-feature=on'/
>> 'hv-feature=off'.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  target/i386/cpu.c     | 28 +++++++++++++++++++++++++++-
>>  target/i386/kvm/kvm.c |  4 ++++
>>  2 files changed, 31 insertions(+), 1 deletion(-)
>> 
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index e8a004c39d04..f8df2caed779 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -4725,6 +4725,29 @@ static void x86_hv_stimer_direct_set(Object *obj, bool value, Error **errp)
>>      x86_hv_feature_set(obj, value, HYPERV_FEAT_STIMER_DIRECT);
>>  }
>>  
>> +static bool x86_hv_passthrough_get(Object *obj, Error **errp)
>> +{
>> +    X86CPU *cpu = X86_CPU(obj);
>> +
>> +    return cpu->hyperv_passthrough;
>> +}
>> +
>> +static void x86_hv_passthrough_set(Object *obj, bool value, Error **errp)
>> +{
>> +    X86CPU *cpu = X86_CPU(obj);
>> +
>> +    cpu->hyperv_passthrough = value;
>> +
>> +    /* hv-passthrough overrides everything with what's supported by the host */
>> +    if (value) {
>> +        cpu->hyperv_features = 0;
>> +        cpu->hyperv_features_on = 0;
>> +        cpu->hyperv_features_off = 0;
>
> why do we have _on|_off fields?
>

You mean 'why do we have them at all' or 'why do we reset them here'?
For the former, we need to distinguish between
'hv-passthroug,hv-feature=off' and just 'hv-passthrough';
'hv-passthrough,hv-evmcs=on' and just 'hv-passthrough'. For the later,
I'd like to make the samentics you've asked for:
'hv-feature,hv-passthrough' == 'hv-passthrough'
(though I still see it as a gotcha for an unprepared user)


>> +    }
>> +
>> +    return;
>> +}
>> +
>>  /* Generic getter for "feature-words" and "filtered-features" properties */
>>  static void x86_cpu_get_feature_words(Object *obj, Visitor *v,
>>                                        const char *name, void *opaque,
>> @@ -7281,7 +7304,6 @@ static Property x86_cpu_properties[] = {
>>                         HYPERV_SPINLOCK_NEVER_NOTIFY),
>>      DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU,
>>                              hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF),
>> -    DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false),
>>  
>>      DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, true),
>>      DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),
>> @@ -7460,6 +7482,10 @@ static void x86_cpu_common_class_init(ObjectClass *oc, void *data)
>>                                     x86_hv_stimer_direct_get,
>>                                     x86_hv_stimer_direct_set);
>>  
>> +    object_class_property_add_bool(oc, "hv-passthrough",
>> +                                   x86_hv_passthrough_get,
>> +                                   x86_hv_passthrough_set);
>> +
>>      for (w = 0; w < FEATURE_WORDS; w++) {
>>          int bitnr;
>>          for (bitnr = 0; bitnr < 64; bitnr++) {
>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
>> index 30013f0d7cee..fca088d4d3b5 100644
>> --- a/target/i386/kvm/kvm.c
>> +++ b/target/i386/kvm/kvm.c
>> @@ -1153,6 +1153,10 @@ static int hv_cpuid_check_and_set(CPUState *cs, int feature, Error **errp)
>>          return 0;
>>      }
>>  
>> +    if (cpu->hyperv_passthrough && (cpu->hyperv_features_off & BIT(feature))) {
>> +        return 0;
>> +    }
>> +
>>      deps = kvm_hyperv_properties[feature].dependencies;
>>      while (deps) {
>>          dep_feat = ctz64(deps);
>

-- 
Vitaly