Re: [PATCH v6 1/5] hw/arm/virt: Only describe cpu topology since virt-6.2

[Andrew Jones]

On Tue, Aug 24, 2021 at 08:20:12PM +0800, Yanan Wang wrote:
> On existing older machine types, without cpu topology described
> in ACPI or DT, the guest will populate one by default. With the
> topology described, it will read the information and set up its
> topology as instructed, but that may not be the same as what was
> getting used by default. It's possible that an user application
> has a dependency on the default topology and if the default one
> gets changed it will probably behave differently.
> 
> Based on above consideration we'd better only describe topology
> information to the guest on 6.2 and later machine types.
> 
> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> ---
>  hw/arm/virt.c         | 3 +++
>  include/hw/arm/virt.h | 4 +++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index ae029680da..82f2eba6bd 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2795,9 +2795,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(6, 2)
>  
>  static void virt_machine_6_1_options(MachineClass *mc)
>  {
> +    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
> +
>      virt_machine_6_2_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_6_1, hw_compat_6_1_len);
>      mc->smp_props.prefer_sockets = true;
> +    vmc->no_cpu_topology = true;
>  }
>  DEFINE_VIRT_MACHINE(6, 1)
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index 9661c46699..6ab21ea90e 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -124,11 +124,13 @@ struct VirtMachineClass {
>      bool claim_edge_triggered_timers;
>      bool smbios_old_sys_ver;
>      bool no_highmem_ecam;
> -    bool no_ged;   /* Machines < 4.2 has no support for ACPI GED device */
> +    bool no_ged;   /* Machines < 4.2 have no support for ACPI GED device */
>      bool kvm_no_adjvtime;
>      bool no_kvm_steal_time;
>      bool acpi_expose_flash;
>      bool no_secure_gpio;
> +    /* Machines < 6.2 have no support for describing cpu topology to guest */
> +    bool no_cpu_topology;
>  };
>  
>  struct VirtMachineState {
> -- 
> 2.19.1
>

Reviewed-by: Andrew Jones <drjones@redhat.com>