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

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

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?

> 
> Jan

-- 
Best regards,
Jiqian Chen.