Re: [PATCH RFC v3 23/23] i386: provide simple 'hyperv=on' option to x86 machine types

[Vitaly Kuznetsov]

Eduardo Habkost <ehabkost@redhat.com> writes:

> On Fri, Oct 09, 2020 at 02:18:42PM +0200, Vitaly Kuznetsov 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 a 'hv_passthrough' mode enabling
>> everything but it can't be used in production as it prevents migration.
>> 
>> Introduce a simple 'hyperv=on' option for all x86 machine types enabling
>> all currently supported Hyper-V enlightenments. Later, when new
>> enlightenments get implemented, we will be adding them to newer machine
>> types only (by disabling them for legacy machine types) thus preserving
>> migration.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>
> This patch seems to be especially useful, and I wonder if we
> could make sure this is included before all the rest of the
> series.  Especially considering that the KVM changes might take a
> while to be merged.

The required KVM changes are queued for 5.11 and I was delaying next
submission till then.

>
> Would you be able to submit this independently from the rest of
> the series?  You can add my:
>
> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
>
> My only (minor) suggestion is to rename
> X86MachineClass.hyperv_features to
> X86MachineClass.default_hyperv_features.

Sure, will do. I'll probably pick a few small patches from the series
(e.g. the one bringing x86_cpu_hyperv_realize()) to minimize the code
churn in the future.

>
>> ---
>>  docs/hyperv.txt       |  8 ++++++++
>>  hw/i386/x86.c         | 30 ++++++++++++++++++++++++++++++
>>  include/hw/i386/x86.h |  7 +++++++
>>  target/i386/cpu.c     | 14 ++++++++++++++
>>  4 files changed, 59 insertions(+)
>> 
>> diff --git a/docs/hyperv.txt b/docs/hyperv.txt
>> index 5df00da54fc4..1a76a07f8417 100644
>> --- a/docs/hyperv.txt
>> +++ b/docs/hyperv.txt
>> @@ -29,6 +29,14 @@ When any set of the Hyper-V enlightenments is enabled, 
>> QEMU changes hypervisor
>>  identification (CPUID 0x40000000..0x4000000A) to Hyper-V. KVM identification
>>  and features are kept in leaves 0x40000100..0x40000101.
>>  
>> +Hyper-V enlightenments can be enabled in bulk by specifying 'hyperv=on' to 
>> an
>> +x86 machine type:
>> +
>> +  qemu-system-x86_64 -machine q35,accel=kvm,kernel-irqchip=split,hyperv=on 
>> ...
>> +
>> +Note, new enlightenments are only added to the latest (in-develompent) 
>> machine
>> +type, older machine types keep the list of the supported features intact to
>> +safeguard migration.
>>  
>>  3. Existing enlightenments
>>  ===========================
>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
>> index 3137a2008588..eeecd4e3322f 100644
>> --- a/hw/i386/x86.c
>> +++ b/hw/i386/x86.c
>> @@ -1171,6 +1171,20 @@ static void x86_machine_set_acpi(Object *obj, Visitor 
>> *v, const char *name,
>>      visit_type_OnOffAuto(v, name, &x86ms->acpi, errp);
>>  }
>>  
>> +static bool x86_machine_get_hyperv(Object *obj, Error **errp)
>> +{
>> +    X86MachineState *x86ms = X86_MACHINE(obj);
>> +
>> +    return x86ms->hyperv_enabled;
>> +}
>> +
>> +static void x86_machine_set_hyperv(Object *obj, bool value, Error **errp)
>> +{
>> +    X86MachineState *x86ms = X86_MACHINE(obj);
>> +
>> +    x86ms->hyperv_enabled = value;
>> +}
>> +
>>  static void x86_machine_initfn(Object *obj)
>>  {
>>      X86MachineState *x86ms = X86_MACHINE(obj);
>> @@ -1193,6 +1207,16 @@ static void x86_machine_class_init(ObjectClass *oc, 
>> void *data)
>>      x86mc->save_tsc_khz = true;
>>      nc->nmi_monitor_handler = x86_nmi;
>>  
>> +    /* Hyper-V features enabled with 'hyperv=on' */
>> +    x86mc->hyperv_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_EVMCS) | BIT(HYPERV_FEAT_IPI) |
>> +        BIT(HYPERV_FEAT_STIMER_DIRECT);
>> +
>>      object_class_property_add(oc, X86_MACHINE_SMM, "OnOffAuto",
>>          x86_machine_get_smm, x86_machine_set_smm,
>>          NULL, NULL);
>> @@ -1204,6 +1228,12 @@ static void x86_machine_class_init(ObjectClass *oc, 
>> void *data)
>>          NULL, NULL);
>>      object_class_property_set_description(oc, X86_MACHINE_ACPI,
>>          "Enable ACPI");
>> +
>> +    object_class_property_add_bool(oc, X86_MACHINE_HYPERV,
>> +        x86_machine_get_hyperv, x86_machine_set_hyperv);
>> +
>> +    object_class_property_set_description(oc, X86_MACHINE_HYPERV,
>> +        "Enable Hyper-V enlightenments");
>>  }
>>  
>>  static const TypeInfo x86_machine_info = {
>> diff --git a/include/hw/i386/x86.h b/include/hw/i386/x86.h
>> index d5dcf7a07fdc..2b989e5fc49d 100644
>> --- a/include/hw/i386/x86.h
>> +++ b/include/hw/i386/x86.h
>> @@ -38,6 +38,9 @@ struct X86MachineClass {
>>      bool save_tsc_khz;
>>      /* Enables contiguous-apic-ID mode */
>>      bool compat_apic_id_mode;
>> +
>> +    /* Hyper-V features enabled with 'hyperv=on' */
>> +    uint64_t hyperv_features;
>>  };
>>  
>>  struct X86MachineState {
>> @@ -70,10 +73,14 @@ struct X86MachineState {
>>       * will be translated to MSI messages in the address space.
>>       */
>>      AddressSpace *ioapic_as;
>> +
>> +    /* Hyper-V emulation */
>> +    bool hyperv_enabled;
>>  };
>>  
>>  #define X86_MACHINE_SMM              "smm"
>>  #define X86_MACHINE_ACPI             "acpi"
>> +#define X86_MACHINE_HYPERV           "hyperv"
>>  
>>  #define TYPE_X86_MACHINE   MACHINE_TYPE_NAME("x86")
>>  OBJECT_DECLARE_TYPE(X86MachineState, X86MachineClass, X86_MACHINE)
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index 55706c8050fe..d0961c1838ad 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -53,6 +53,7 @@
>>  #include "sysemu/tcg.h"
>>  #include "hw/qdev-properties.h"
>>  #include "hw/i386/topology.h"
>> +#include "hw/i386/x86.h"
>>  #ifndef CONFIG_USER_ONLY
>>  #include "exec/address-spaces.h"
>>  #include "hw/i386/apic_internal.h"
>> @@ -6409,8 +6410,21 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool 
>> verbose)
>>  
>>  static void x86_cpu_hyperv_realize(X86CPU *cpu)
>>  {
>> +    X86MachineState *x86ms = X86_MACHINE(qdev_get_machine());
>> +    X86MachineClass *x86mc = X86_MACHINE_GET_CLASS(x86ms);
>> +    uint64_t feat;
>>      size_t len;
>>  
>> +    if (x86ms->hyperv_enabled) {
>> +        feat = x86mc->hyperv_features;
>> +        /* Enlightened VMCS is only available on Intel/VMX */
>> +        if (!cpu_has_vmx(&cpu->env)) {
>> +            feat &= ~BIT(HYPERV_FEAT_EVMCS);
>> +        }
>> +
>> +        cpu->hyperv_features |= feat;
>> +    }
>> +
>>      /* Hyper-V vendor id */
>>      if (!cpu->hyperv_vendor) {
>>          object_property_set_str(OBJECT(cpu), "hv-vendor-id", "Microsoft Hv",
>> -- 
>> 2.25.4
>> 

-- 
Vitaly