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

[Eduardo Habkost]

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().

-- 
Eduardo