Re: [PATCH v2 15/58] i386/tdx: Add property sept-ve-disable for tdx-guest object

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Aug 18, 2023 at 05:49:58AM -0400, Xiaoyao Li wrote:
> Bit 28 of TD attribute, named SEPT_VE_DISABLE. When set to 1, it disables
> EPT violation conversion to #VE on guest TD access of PENDING pages.
> 
> Some guest OS (e.g., Linux TD guest) may require this bit as 1.
> Otherwise refuse to boot.
> 
> Add sept-ve-disable property for tdx-guest object, for user to configure
> this bit.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Acked-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  qapi/qom.json         |  4 +++-
>  target/i386/kvm/tdx.c | 24 ++++++++++++++++++++++++
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 2ca7ce7c0da5..cc08b9a98df9 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -871,10 +871,12 @@
>  #
>  # Properties for tdx-guest objects.
>  #
> +# @sept-ve-disable: bit 28 of TD attributes (default: 0)

This description isn't very useful as it forces the user to go off and
read the TDX specification to find out what bit 28 means. You've got a
more useful description in the commit message, so please use that
in the docs too. eg something like this

  @sept-ve-disable: toggle bit 28 of TD attributes to control disabling
                    of EPT violation conversion to #VE on guest
                    TD access of PENDING pages. Some guest OS (e.g.
		    Linux TD guest) may require this set, otherwise
                    they refuse to boot.

> +#
>  # Since: 8.2
>  ##
>  { 'struct': 'TdxGuestProperties',
> -  'data': { }}
> +  'data': { '*sept-ve-disable': 'bool' } }
>  
>  ##
>  # @ThreadContextProperties:
> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
> index 3d313ed46bd1..22130382c0c5 100644
> --- a/target/i386/kvm/tdx.c
> +++ b/target/i386/kvm/tdx.c
> @@ -32,6 +32,8 @@
>                                       (1U << KVM_FEATURE_PV_SCHED_YIELD) | \
>                                       (1U << KVM_FEATURE_MSI_EXT_DEST_ID))
>  
> +#define TDX_TD_ATTRIBUTES_SEPT_VE_DISABLE   BIT_ULL(28)
> +
>  #define TDX_ATTRIBUTES_MAX_BITS      64
>  
>  static FeatureMask tdx_attrs_ctrl_fields[TDX_ATTRIBUTES_MAX_BITS] = {
> @@ -501,6 +503,24 @@ out:
>      return r;
>  }
>  
> +static bool tdx_guest_get_sept_ve_disable(Object *obj, Error **errp)
> +{
> +    TdxGuest *tdx = TDX_GUEST(obj);
> +
> +    return !!(tdx->attributes & TDX_TD_ATTRIBUTES_SEPT_VE_DISABLE);
> +}
> +
> +static void tdx_guest_set_sept_ve_disable(Object *obj, bool value, Error **errp)
> +{
> +    TdxGuest *tdx = TDX_GUEST(obj);
> +
> +    if (value) {
> +        tdx->attributes |= TDX_TD_ATTRIBUTES_SEPT_VE_DISABLE;
> +    } else {
> +        tdx->attributes &= ~TDX_TD_ATTRIBUTES_SEPT_VE_DISABLE;
> +    }
> +}
> +
>  /* tdx guest */
>  OBJECT_DEFINE_TYPE_WITH_INTERFACES(TdxGuest,
>                                     tdx_guest,
> @@ -516,6 +536,10 @@ static void tdx_guest_init(Object *obj)
>      qemu_mutex_init(&tdx->lock);
>  
>      tdx->attributes = 0;
> +
> +    object_property_add_bool(obj, "sept-ve-disable",
> +                             tdx_guest_get_sept_ve_disable,
> +                             tdx_guest_set_sept_ve_disable);
>  }
>  
>  static void tdx_guest_finalize(Object *obj)
> -- 
> 2.34.1
> 

With regards,
Daniel
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