Re: [PATCH v17 10/20] KVM: arm64: coco: Disable Steal time accounting for coco guests

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 10/09/2026 13:42, Fuad Tabba wrote:
> Hi Suzuki,
> 
> On Thu, 10 Sept 2026 at 11:28, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> ...
>> Just to make sure I understand the picture:
>>
>> For coco VMs:
>>
>>    - check extension on coco KVM, KVM_CAP_STEAL_TIME => 0
>>
>> And a follow up DEVICE_HAS_ATTR => -EPERM ?
>>
>> But we tell the VMM, look you don't have the capabilit on this VM.
>> But if you try to set the attribute isn't it more appropriate to
>> say:
>>    -ENXIO - No you don't have that feature on this VM (-ENXIO)
>> rather than
>>    -EPERM - No, I won't let you do that.
>>
>> Remember we are doing only in the "VM" context. It is a minor nit
>> but I wanted to make sure we understand what we are thinking.
> 
> -ENXIO it is. I went back to api.rst for KVM_SET_DEVICE_ATTR: ENXIO is
> for a group or attribute that's "unknown/unsupported for this device",
> and EPERM for one that "cannot (currently) be accessed this way", a
> state or access-mode refusal, so a VM type that doesn't have the
> feature is the former. KVM_HAS_DEVICE_ATTR only documents ENXIO at
> all. Your patch is good as it is.
> 
> Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>

Cheers,

Suzuki