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

[Jan Beulich <jbeulich@xxxxxxxx>]

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. "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.

Jan