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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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).

Jan


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