Re: [RFC XEN PATCH v4 4/5] domctl: Use gsi to grant/revoke irq permission

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

Thank Jan and Roger, I may know how to add a new hypercall 
XEN_DOMCTL_gsi_permission, I will implement it in next version.

On 2024/1/9 18:46, Jan Beulich wrote:
> On 09.01.2024 11:16, Chen, Jiqian wrote:
>> On 2024/1/9 17:38, Jan Beulich wrote:
>>> On 09.01.2024 09:18, Chen, Jiqian wrote:
>>>> A new hypercall using for granting gsi? If so, how does the caller know to 
>>>> call which hypercall to grant permission, XEN_DOMCTL_irq_permission or 
>>>> that new hypercall?
>>>
>>> Either we add a feature indicator, or the caller simply tries the
>>> new GSI interface first.
>> I am still not sure how to use and implement it.
>> Taking pci_add_dm_done as an example, for now its implementation is:
>> pci_add_dm_done
>>      xc_physdev_map_pirq
>>      xc_domain_irq_permission(,,pirq,)
>>              XEN_DOMCTL_irq_permission
>>
>> And assume the new hypercall is XEN_DOMCTL_gsi_permission, do you mean:
>> pci_add_dm_done
>>      xc_physdev_map_pirq
>>      ret = xc_domain_gsi_permission(,,gsi,)
>>              XEN_DOMCTL_gsi_permission
>>      if ( ret != 0 )
>>              xc_domain_irq_permission(,,pirq,)
>>                      XEN_DOMCTL_irq_permission
> 
> No, falling back shouldn't be "blind". Fallback should only happen
> when the new sub-op isn't implemented (hence why a feature indicator
> may be necessary), and only if calling the existing sub-op promises
> to be useful (which iirc would limit that to the PV Dom0 case).
> 
>> But if so, I have a question that in XEN_DOMCTL_gsi_permission, when to fail 
>> and when to success?
> 
> I'm afraid I don't understand the question. Behavior there isn't to
> be fundamentally different from that for XEN_DOMCTL_irq_permission.
> It's just that the incoming value is in another value space.
> 
>> Or do you mean:
>> pci_add_dm_done
>>      xc_physdev_map_pirq
>>      ret = xc_domain_irq_permission(,,pirq,)
>>              XEN_DOMCTL_irq_permission
>>      if ( ret != 0 )
>>              xc_domain_gsi_permission(,,gsi,)
>>                      XEN_DOMCTL_gsi_permission
> 
> No, this looks the wrong way round.
> 
>> And in XEN_DOMCTL_gsi_permission, as long as the current domain has the 
>> access of gsi, then granting gsi to caller should be successful. Right?
> 
> I think so; see above.
> 
> Jan

-- 
Best regards,
Jiqian Chen.