Re: [Xen-devel] [PATCH v11 2/6] VT-d: Introduce new fields in msi_desc to track binding with guest interrupt

[Chao Gao <chao.gao@xxxxxxxxx>]

On Fri, Mar 31, 2017 at 02:11:08AM -0600, Jan Beulich wrote:
>>>> On 31.03.17 at 01:01, <chao.gao@xxxxxxxxx> wrote:
>> On Fri, Mar 31, 2017 at 01:46:33PM +0800, Tian, Kevin wrote:
>>>> From: Gao, Chao
>>>> Sent: Wednesday, March 29, 2017 1:12 PM
>>>> --- a/xen/drivers/passthrough/io.c
>>>> +++ b/xen/drivers/passthrough/io.c
>>>> @@ -618,6 +618,8 @@ int pt_irq_destroy_bind(
>>>>          else
>>>>              what = "bogus";
>>>>      }
>>>> +    else if ( iommu_intpost && pirq && pirq_dpci->gmsi.posted )
>>>
>>>No need to check iommu_intpost. Just keep later conditions.
>> 
>> ok. Is it for if posted is set, the iommu_intpost should be true?
>> 
>>>
>>>btw isn't the condition be " (pirq_dpci && pirq_dpci->gmsi.posted)"?
>> 
>> I don't think so. pirq, not pirq_dpci, is consumed by pi_update_irte.
>> Furthermore if pirq_dpci is null, pirq is also null. But it is not true
>> in turn.
>
>With
>
>    pirq_dpci = pirq_dpci(pirq);
>
>it _is_ the other way around, which can then also be expressed
>as "if pirq_dpci is non-NULL, pirq is non-NULL too", which is the
>precondition you need to consume (dereference) pirq. There is
>a reason other code around here also only ever checks pirq_dpci
>(even when using pirq).

Got it. Kevin and you are right.

Thanks
Chao

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