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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.05.2024 08:56, Chen, Jiqian wrote:
> 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.

What are you taking this from? The loop bound isn't nr_gsis, and the iteration
variable isn't in GSI space either; it's in IRQ numbering space. In this loop
we're merely leveraging that every GSI has a corresponding IRQ; there are no
assumptions made about the mapping between the two. Afaics at least.

>> "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.

I did point you at the ACPI Interrupt Source Override structure before.
We're parsing those in acpi_parse_int_src_ovr(), to give you a place to
start going from.

Jan