RE: [PATCH 1/2] hyperv: Sync guest VMM capabilities structure with Microsoft Hypervisor ABI

[Michael Kelley]

From: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx> Sent: Wednesday, January 21, 2026 2:36 PM
> 
> From: Andreea Pintilie <anpintil@xxxxxxxxxxxxx>
> 
> Update the partition VMM capability structure to match the hypervisor
> representation to bring it to the up to date state. A precursor patch for
> Root-on-Core scheduler feature support.
> 
> Signed-off-by: Andreea Pintilie <anpintil@xxxxxxxxxxxxx>
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx>
> ---
>  include/hyperv/hvhdk_mini.h |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/hyperv/hvhdk_mini.h b/include/hyperv/hvhdk_mini.h
> index 41a29bf8ec14..aa03616f965b 100644
> --- a/include/hyperv/hvhdk_mini.h
> +++ b/include/hyperv/hvhdk_mini.h
> @@ -102,7 +102,7 @@ enum hv_partition_property_code {
>  };
> 
>  #define HV_PARTITION_VMM_CAPABILITIES_BANK_COUNT		1
> -#define HV_PARTITION_VMM_CAPABILITIES_RESERVED_BITFIELD_COUNT	59
> +#define HV_PARTITION_VMM_CAPABILITIES_RESERVED_BITFIELD_COUNT	58
> 
>  struct hv_partition_property_vmm_capabilities {
>  	u16 bank_count;
> @@ -119,6 +119,7 @@ struct hv_partition_property_vmm_capabilities {
>  			u64 reservedbit3: 1;
>  #endif
>  			u64 assignable_synthetic_proc_features: 1;
> +			u64 tag_hv_message_from_child: 1;
>  			u64 reserved0: HV_PARTITION_VMM_CAPABILITIES_RESERVED_BITFIELD_COUNT;
>  		} __packed;
>  	};

The tag_hv_message_from_child field is not used in the 2nd patch of this
patch set, so it is added but never used. Is it added just to be a placeholder
so that field vmm_enable_integrated_scheduler can be added in the 2nd patch?
If that's the case, I'd suggest dropping this patch, and have the 2nd patch
add a "reservedbit5" field along with vmm_enable_integrated_scheduler.

If later there is a use for tag_hv_message_from_child, the "reservedbit5"
field can be renamed at that time.

Michael