Re: [Xen-devel] [PATCH v11 1/6] passthrough: don't migrate pirq when it is delivered through VT-d PI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.03.17 at 04:42, <chao.gao@xxxxxxxxx> wrote:
> On Fri, Mar 31, 2017 at 03:31:47AM -0600, Jan Beulich wrote:
>>>>> On 29.03.17 at 07:11, <chao.gao@xxxxxxxxx> wrote:
>>> @@ -442,17 +397,24 @@ int pt_irq_create_bind(
>>>          dest_vcpu_id = hvm_girq_dest_2_vcpu_id(d, dest, dest_mode);
>>>          pirq_dpci->gmsi.dest_vcpu_id = dest_vcpu_id;
>>>          spin_unlock(&d->event_lock);
>>> +
>>> +        pirq_dpci->gmsi.posted = false;
>>> +        vcpu = (dest_vcpu_id >= 0) ? d->vcpu[dest_vcpu_id] : NULL;
>>> +        if ( iommu_intpost && (delivery_mode == dest_LowestPrio) )
>>
>>Why again would dest_Fixed not allow posted delivery? This needs
> 
> No this restriction. For dest_Fixed case, hvm_girq_dest_2_vcpu_id() gives
> the same output with pi_find_dest_vcpu(). Thus we don't call it again, just
> use the return value of hvm_girq_dest_2_vcpu_id().

But as pointed out you don't set the new posted field in that case.

>>recording in a comment, if there really is such a restriction. Or did
>>you really mean to place ...
>>
>>> +        {
>>> +            vcpu = vector_hashing_dest(d, dest, dest_mode,
>>> +                                       pirq_dpci->gmsi.gvec);
>>> +            if ( vcpu )
>>> +                pirq_dpci->gmsi.posted = true;
>>
>>... this ...
>>
>>> +        }
>>
>>... after this brace (which then wouldn't be needed anymore)? If
>>so, is there any point calling vector_hashing_dest() when vcpu is
>>already non-NULL prior to the if()?
>>
>>This then also raises the question whether the call to
>>hvm_girq_dest_2_vcpu_id() is actually legitimate for lowest
>>priority delivery mode.
> 
> For lowest priority delivery mode, if VT-d PI is enabled, the result (the
> destination vcpu) is overrided by vector_hashing_dest() to keep the 
> existing behavior. I think the only point we should keep in mind is
> for cases other than lowest priority delivery mode, pi_find_dest_vcpu()
> and hvm_girq_dest_2_vcpu_id() give the same destination vcpu.

Well, the override is done for the iommu_intpost case. The remark
on hvm_girq_dest_2_vcpu_id(), however, was made in general.

Jan


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