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

[Igor Mammedov]

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?

> +    }
> +
> +    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);