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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 30.05.2024 13:19, Chen, Jiqian wrote:
> On 2024/5/29 20:22, Jan Beulich wrote:
>> On 29.05.2024 13:13, Chen, Jiqian wrote:
>>> 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:
>>>>>>> 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?
>>
>> This looks plausible, yes.
> I dump all mpc_config_intsrc of array mp_irqs, it shows:
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 0 dstapic 
> 33 dstirq 2
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 15 srcbus 0 srcbusirq 9 dstapic 
> 33 dstirq 9
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 1 dstapic 
> 33 dstirq 1
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 3 dstapic 
> 33 dstirq 3
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 4 dstapic 
> 33 dstirq 4
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 5 dstapic 
> 33 dstirq 5
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 6 dstapic 
> 33 dstirq 6
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 7 dstapic 
> 33 dstirq 7
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 8 dstapic 
> 33 dstirq 8
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 10 dstapic 
> 33 dstirq 10
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 11 dstapic 
> 33 dstirq 11
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 12 dstapic 
> 33 dstirq 12
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 13 dstapic 
> 33 dstirq 13
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 14 dstapic 
> 33 dstirq 14
> (XEN) find_irq_entry type 3 irqtype 0 irqflag 0 srcbus 0 srcbusirq 15 dstapic 
> 33 dstirq 15
> 
> It seems only Legacy irq and gsi[0:15] has a mapping in mp_irqs.
> Other gsi can be considered 1:1 mapping with irq? Or are there other places 
> reflect the mapping between irq and gsi?

It may be uncommon to have overrides for higher GSIs, but I don't think ACPI
disallows that.

Jan