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

[David Edmondson <dme@dme.org>]

On Friday, 2021-02-12 at 09:49:46 +01, Vitaly Kuznetsov wrote:

> 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)

Either approach will confuse *someone*, I think.

This way at least behaves better if someone/something is composing the
feature strings via concatenation.

>>> +    }
>>> +
>>> +    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

dme.
-- 
J'aurais toujours faim de toi.