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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 04.06.2024 05:04, Chen, Jiqian wrote:
> On 2024/5/30 23:51, Jan Beulich wrote:
>> 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.
> Do you suggest me to add overrides for higher GSIs into array mp_irqs?

Why "add"? That's what mp_override_legacy_irq() already does, isn't it?
Assuming of course any are surfaced at all by ACPI.

Jan