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

[Chao Gao <chao.gao@xxxxxxxxx>]

On Fri, Mar 31, 2017 at 01:28:02PM +0800, Tian, Kevin wrote:
>> From: Chao Gao
>> Sent: Wednesday, March 29, 2017 1:12 PM
>> 
>> When a vCPU migrated to another pCPU, pt irqs binded to this vCPU also
>> needed migration. When VT-d PI is enabled, interrupt vector will be recorded
>> to a main memory resident data-structure and a notification whose
>> destination is decided by NDST is generated. NDST is properly adjusted
>> during vCPU migration so pirq directly injected to guest needn't be migrated.
>> 
>> This patch adds a indicator, @posted, to show whether the pt irq is delivered
>> through VT-d PI.
>> 
>> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
>> 
>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index
>> 0282986..2d8de16 100644
>> --- 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) )
>
>simply looking at above change it's more than what you intend to change.
>Previously even w/o GUEST_MSI flag will fall into that path, but now
>you limit it to only GUEST_MSI and irq remapping (i.e. changed the
>behavior for both posted case and w/o GUEST_MSI case). I haven't looked
>whether MACH_MASI always set with GUEST_MSI, but my gut-feeling 
>looks not correct here.

Yes. It's a problem. I think the original code may be wrong for it acquires
gmsi.dest_vcpu_id without checking 'flags' of pirq_dpci. Do we need to migrate
pirq when its type is GUEST_PCI?

Thanks
Chao

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