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

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2024/6/4 13:55, Jan Beulich wrote:
> 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?
No. mp_override_legacy_irq only overrides for gsi < 16, but not for gsi >= 16(I 
dump all mappings from array mp_irqs).
In my environment, gsi of my dGPU is 24.
So, how do I process for gsi >= 16?

> Assuming of course any are surfaced at all by ACPI.
> 
> Jan

-- 
Best regards,
Jiqian Chen.