Re: [Xen-devel] [PATCH v12 1/7] passthrough: don't migrate pirq when it is delivered through VT-d PI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.04.17 at 06:07, <chao.gao@xxxxxxxxx> wrote:
> Cc: kevin
> 
> On Fri, Apr 07, 2017 at 04:38:00AM -0600, Jan Beulich wrote:
>>>>> On 06.04.17 at 02:30, <chao.gao@xxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/hvm/hvm.c
>>> +++ b/xen/arch/x86/hvm/hvm.c
>>> @@ -438,6 +438,9 @@ static int hvm_migrate_pirq(struct domain *d, struct 
> hvm_pirq_dpci *pirq_dpci,
>>>      struct vcpu *v = arg;
>>>  
>>>      if ( (pirq_dpci->flags & HVM_IRQ_DPCI_MACH_MSI) &&
>>> +         (pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI) &&
>>> +         /* Needn't migrate pirq if this pirq is delivered to guest 
> directly.*/
>>> +         (!pirq_dpci->gmsi.posted) &&
>>>           (pirq_dpci->gmsi.dest_vcpu_id == v->vcpu_id) )
>>>      {
>>
>>I don't think I've seen you address Kevin's comment on this for v11,
>>and like Kevin I can't immediately see why the above addition would
>>be correct. Do you perhaps mean
>>
>>    if ( (pirq_dpci->flags & HVM_IRQ_DPCI_MACH_MSI) &&
>>         /* Needn't migrate pirq if this pirq is delivered to guest 
>> directly.*/
>>         (!pirq_dpci->gmsi.posted ||
>>          <whatever is appropriate here, if anything>) &&
>>         (pirq_dpci->gmsi.dest_vcpu_id == v->vcpu_id) )
> 
> Sorry to Kevin. And thanks to point it out. 
> But I thought we had discussed this in 
> https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg04383.html. I 
> did think you agreed with me.
> gmsi is invalid when pirq_dpci is not GUEST_MSI, is there something I have
> ignored?

You've been talking about GUEST_PCI there, which I did (and do)
agree we can't handle here. So for the purposes of your series,
simply adding the gmsi.posted check would be the right thing imo.
I don't think I see anything wrong with the ->gmsi accesses here:
The GUEST_PCI code simply doesn't set them, so dest_vcpu_id
will still be -1 (from pt_pirq_init()). So I don't see any bug being
fixed here with the extra other check you add. If you agree, I
can take that line and the commit message sentence out while
committing.

Jan


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