Re: [PATCH 5/5] i386: provide simple 'hyperv=on' option to x86 machine types

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Eduardo Habkost <ehabkost@redhat.com> writes:

> On Thu, Nov 19, 2020 at 11:32:21AM +0100, 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>
>> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> [...]
>> ---
>>  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 5944fc44edca..57f27d56ecc6 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);
>> @@ -1194,6 +1208,16 @@ 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->default_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);
>> @@ -1205,6 +1229,12 @@ 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 739fac50871b..598abd1be806 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 default_hyperv_features;
>>  };
>>  
>>  struct X86MachineState {
>> @@ -71,10 +74,14 @@ 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 83aca942d87c..63a931679d73 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"
>> @@ -6511,8 +6512,21 @@ 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->default_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;
>> +    }
>
> I had to dequeue this because it doesn't compile with
> CONFIG_USER_ONLY:
>
> https://gitlab.com/ehabkost/qemu/-/jobs/916651017
>
> The easiest solution would be to wrap the new code in #ifndef
> CONFIG_USER_ONLY, but maybe we should try to move all
> X86Machine-specific code from cpu.c to
> hw/i386/x86.c:x86_cpu_pre_plug().

Bummer, 

let me try the suggestion.

-- 
Vitaly