Re: [PATCH v4 20/21] i386: provide simple 'hv-default=on' option

[Vitaly Kuznetsov]

Igor Mammedov <imammedo@redhat.com> writes:

> On Wed, 10 Feb 2021 17:40:32 +0100
> Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
>> Enabling Hyper-V emulation for a Windows VM is a tiring experience as it
>> requires listing all currently supported enlightenments ("hv-*" CPU
>> features) explicitly. We do have 'hv-passthrough' mode enabling
>> everything but it can't be used in production as it prevents migration.
>> 
>> Introduce a simple 'hv-default=on' CPU flag enabling all currently supported
>> Hyper-V enlightenments. Later, when new enlightenments get implemented,
>> compat_props mechanism will be used to disable them for legacy machine types,
>> this will keep 'hv-default=on' configurations migratable.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  docs/hyperv.txt   | 16 ++++++++++++---
>>  target/i386/cpu.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++
>>  target/i386/cpu.h |  3 +++
>>  3 files changed, 68 insertions(+), 3 deletions(-)
>> 
>> diff --git a/docs/hyperv.txt b/docs/hyperv.txt
>> index 5df00da54fc4..a54c066cab09 100644
>> --- a/docs/hyperv.txt
>> +++ b/docs/hyperv.txt
>> @@ -17,10 +17,20 @@ compatible hypervisor and use Hyper-V specific features.
>>  
>>  2. Setup
>>  =========
>> -No Hyper-V enlightenments are enabled by default by either KVM or QEMU. In
>> -QEMU, individual enlightenments can be enabled through CPU flags, e.g:
>> +All currently supported Hyper-V enlightenments can be enabled by specifying
>> +'hv-default=on' CPU flag:
>>  
>> -  qemu-system-x86_64 --enable-kvm --cpu host,hv_relaxed,hv_vpindex,hv_time, 
>> ...
>> +  qemu-system-x86_64 --enable-kvm --cpu host,hv-default ...
>> +
>> +Alternatively, it is possible to do fine-grained enablement through CPU 
>> flags,
>> +e.g:
>> +
>> +  qemu-system-x86_64 --enable-kvm --cpu host,hv-relaxed,hv-vpindex,hv-time 
>> ...
>> +
>> +It is also possible to disable individual enlightenments from the default 
>> list,
>> +this can be used for debugging purposes:
>> +
>> +  qemu-system-x86_64 --enable-kvm --cpu host,hv-default=on,hv-evmcs=off ...
>>  
>>  Sometimes there are dependencies between enlightenments, QEMU is supposed to
>>  check that the supplied configuration is sane.
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index f8df2caed779..013aa60272d8 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -4736,6 +4736,12 @@ static void x86_hv_passthrough_set(Object *obj, bool 
>> value, Error **errp)
>>  {
>>      X86CPU *cpu = X86_CPU(obj);
>>  
>> +    if (cpu->hyperv_default) {

^^^ here ^^^

>> +        error_setg(errp,
>> +                   "'hv-default' and 'hv-paththrough' are mutually 
>> exclusive");
>> +        return;
>> +    }
>> +
>>      cpu->hyperv_passthrough = value;
>>  
>>      /* hv-passthrough overrides everything with what's supported by the 
>> host */
>> @@ -4748,6 +4754,33 @@ static void x86_hv_passthrough_set(Object *obj, bool 
>> value, Error **errp)
>>      return;
>>  }
>>  
>> +static bool x86_hv_default_get(Object *obj, Error **errp)
>> +{
>> +    X86CPU *cpu = X86_CPU(obj);
>> +
>> +    return cpu->hyperv_default;
>> +}
>> +
>> +static void x86_hv_default_set(Object *obj, bool value, Error **errp)
>> +{
>> +    X86CPU *cpu = X86_CPU(obj);
>> +
>> +    if (cpu->hyperv_passthrough) {
>> +        error_setg(errp,
>> +                   "'hv-default' and 'hv-paththrough' are mutually 
>> exclusive");
> this check will work only half way, i.e.: hv-paththrough=on,hv-default=on|off
> (where off value looks a bit wierd)
> but not other way around: hv-default=on,hv-paththrough=on

The check in x86_hv_passthrough_set() chechs the opposite scenario.

>
> were you thinking about following error:
>   "hv-default can't be used after hv-paththrough were enabled"
>
> or if it symmetric, then putting this check in realizefn() will do the job
> as both properties are processed by that time.

I can move the check there but I think that two checks I add here cover
what we need (and we don't need to care what to set 'hyperv_features' to
in the interim).

>
>> +        return;
>> +    }
>> +
>> +    cpu->hyperv_default = value;
>> +
>> +    /* hv-default overrides everything with the default set */
>> +    if (value) {
>> +        cpu->hyperv_features = cpu->hyperv_default_features;
>> +        cpu->hyperv_features_on = 0;
>> +        cpu->hyperv_features_off = 0;
>> +    }
>> +}
>> +
>>  /* 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,
>> @@ -7152,6 +7185,21 @@ static void x86_cpu_initfn(Object *obj)
>>      if (xcc->model) {
>>          x86_cpu_load_model(cpu, xcc->model);
>>      }
>> +
>> +    /* Hyper-V features enabled with 'hv-default=on' */
>> +    cpu->hyperv_default_features = BIT(HYPERV_FEAT_RELAXED) |
>> +        BIT(HYPERV_FEAT_VAPIC) | BIT(HYPERV_FEAT_TIME) |
>> +        BIT(HYPERV_FEAT_CRASH) | BIT(HYPERV_FEAT_RESET) |
>> +        BIT(HYPERV_FEAT_VPINDEX) | BIT(HYPERV_FEAT_RUNTIME) |
>> +        BIT(HYPERV_FEAT_SYNIC) | BIT(HYPERV_FEAT_STIMER) |
>> +        BIT(HYPERV_FEAT_FREQUENCIES) | BIT(HYPERV_FEAT_REENLIGHTENMENT) |
>> +        BIT(HYPERV_FEAT_TLBFLUSH) | BIT(HYPERV_FEAT_IPI) |
>> +        BIT(HYPERV_FEAT_STIMER_DIRECT);
>> +
>> +    /* Enlightened VMCS is only available on Intel/VMX */
>> +    if (kvm_hv_evmcs_available()) {
>> +        cpu->hyperv_default_features |= BIT(HYPERV_FEAT_EVMCS);
>> +    }
>>  }
>>  
>>  static int64_t x86_cpu_get_arch_id(CPUState *cs)
>> @@ -7486,6 +7534,10 @@ static void x86_cpu_common_class_init(ObjectClass 
>> *oc, void *data)
>>                                     x86_hv_passthrough_get,
>>                                     x86_hv_passthrough_set);
>>  
>> +    object_class_property_add_bool(oc, "hv-default",
>> +                              x86_hv_default_get,
>> +                              x86_hv_default_set);
>> +
>>      for (w = 0; w < FEATURE_WORDS; w++) {
>>          int bitnr;
>>          for (bitnr = 0; bitnr < 64; bitnr++) {
>> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
>> index b4fbd46f0fc9..59350e70fb51 100644
>> --- a/target/i386/cpu.h
>> +++ b/target/i386/cpu.h
>> @@ -1670,6 +1670,9 @@ struct X86CPU {
>>      uint64_t hyperv_features_on;
>>      uint64_t hyperv_features_off;
>>      bool hyperv_passthrough;
>> +    /* 'hv-default' enablement */
>> +    uint64_t hyperv_default_features;
>> +    bool hyperv_default;
>>      OnOffAuto hyperv_no_nonarch_cs;
>>      uint32_t hyperv_vendor_id[3];
>>      uint32_t hyperv_interface_id[4];
>

-- 
Vitaly