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 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?
And my code will be:
    case XEN_DOMCTL_gsi_permission:
    {
        unsigned int gsi = domctl->u.gsi_permission.gsi;
        int irq;
        bool allow = domctl->u.gsi_permission.allow_access;

        /*
         * gsi[0,15] is not 1:1 mapping to legacy irq[0,15], it need a
         * transformation. Other gsi is considered be 1:1 mapping to irq
         */
        if ( gsi < 16 )
            irq = gsi_2_irq(gsi);
        else
            irq = gsi;

        /*
         * If current domain is PV or it has PIRQ flag, it has a mapping
         * of gsi, pirq and irq, so it should use XEN_DOMCTL_irq_permission
         * to grant irq permission.
         */
        if ( is_pv_domain(current->domain) || has_pirq(current->domain) )
        {
            ret = -EOPNOTSUPP;
            break;
        }

        if ( gsi >= nr_irqs_gsi || irq < 0 )
        {
            ret = -EINVAL;
            break;
        }

        if ( !irq_access_permitted(current->domain, irq) ||
             xsm_irq_permission(XSM_HOOK, d, irq, allow) )
        {
            ret = -EPERM;
            break;
        }

        if ( allow )
            ret = irq_permit_access(d, irq);
        else
            ret = irq_deny_access(d, irq);
        break;
    }

Is above acceptable?

> 
> Jan

-- 
Best regards,
Jiqian Chen.