Re: [RFC XEN PATCH v8 5/5] domctl: Add XEN_DOMCTL_gsi_permission to grant gsi

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

On 2024/5/29 14:31, Jan Beulich wrote:
> On 29.05.2024 04:41, Chen, Jiqian wrote:
>> Hi,
>> On 2024/5/17 19:50, Jan Beulich wrote:
>>> On 17.05.2024 13:14, Chen, Jiqian wrote:
>>>> On 2024/5/17 18:51, Jan Beulich wrote:
>>>>> On 17.05.2024 12:45, Chen, Jiqian wrote:
>>>>>> On 2024/5/16 22:01, Jan Beulich wrote:
>>>>>>> On 16.05.2024 11:52, Jiqian Chen wrote:
>>>>>>>> +        if ( gsi >= nr_irqs_gsi )
>>>>>>>> +        {
>>>>>>>> +            ret = -EINVAL;
>>>>>>>> +            break;
>>>>>>>> +        }
>>>>>>>> +
>>>>>>>> +        if ( !irq_access_permitted(current->domain, gsi) ||
>>>>>>>
>>>>>>> I.e. assuming IRQ == GSI? Is that a valid assumption when any number of
>>>>>>> source overrides may be surfaced by ACPI?
>>>>>> All irqs smaller than nr_irqs_gsi are gsi, aren't they?
>>>>>
>>>>> They are, but there's not necessarily a 1:1 mapping.
>>>> Oh, so do I need to add a new gsi_caps to store granted gsi?
>>>
>>> Probably not. You ought to be able to translate between GSI and IRQ,
>>> and then continue to record in / check against IRQ permissions.
>> But I found in function init_irq_data:
>>     for ( irq = 0; irq < nr_irqs_gsi; irq++ )
>>     {
>>         int rc;
>>
>>         desc = irq_to_desc(irq);
>>         desc->irq = irq;
>>
>>         rc = init_one_irq_desc(desc);
>>         if ( rc )
>>             return rc;
>>     }
>> Does it mean that when irq < nr_irqs_gsi, the gsi and irq is a 1:1 mapping?
> 
> No, as explained before. I also don't see how you would derive that from the 
> code above.
Because here set desc->irq = irq, and it seems there is no other place to 
change this desc->irq, so, gsi 1 is considered to irq 1.

> "nr_irqs_gsi" describes what its name says: The number of
> IRQs mapping to a (_some_) GSI. That's to tell them from the non-GSI (i.e.
> mainly MSI) ones. There's no implication whatsoever on the IRQ <-> GSI
> mapping.
> 
>> What's more, when using PHYSDEVOP_setup_gsi, it calls mp_register_gsi,
>> and in mp_register_gsi, it uses " desc = irq_to_desc(gsi); " to get irq_desc 
>> directly.
> 
> Which may be wrong, while that wrong-ness may not have hit anyone in
> practice (for reasons that would need working out).
> 
>> Combining above, can we consider "gsi == irq" when irq < nr_irqs_gsi ?
> 
> Again - no.
Since you are certain that they are not equal, could you tell me where show 
they are not equal or where build their mappings,
so that I can know how to do a conversion gsi from irq.

> 
> Jan

-- 
Best regards,
Jiqian Chen.