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 15:10, Jan Beulich wrote:
> 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.
Oh! I think I know.
If I want to transform gsi to irq, I need to do below:
        int irq, entry, ioapic, pin;

        ioapic = mp_find_ioapic(gsi);
        pin = gsi - mp_ioapic_routing[ioapic].gsi_base;
        entry = find_irq_entry(ioapic, pin, mp_INT);
        irq = pin_2_irq(entry, ioapic, pin);

Am I right?

> 
> Jan

-- 
Best regards,
Jiqian Chen.