netdev - Re: [PATCH 2/7] kvm/vfio: detect assigned device via irqbypass manager

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Date:   Mon, 13 Jul 2020 16:13:35 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>
Cc:     alex.williamson@...hat.com, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, dan.daly@...el.com
Subject: Re: [PATCH 2/7] kvm/vfio: detect assigned device via irqbypass
 manager


On 2020/7/13 上午5:06, Michael S. Tsirkin wrote:
> On Sun, Jul 12, 2020 at 10:49:21PM +0800, Zhu Lingshan wrote:
>> We used to detect assigned device via VFIO manipulated device
>> conters. This is less flexible consider VFIO is not the only
>> interface for assigned device. vDPA devices has dedicated
>> backed hardware as well. So this patch tries to detect
>> the assigned device via irqbypass manager.
>>
>> We will increase/decrease the assigned device counter in kvm/x86.
>> Both vDPA and VFIO would go through this code path.
>>
>> This code path only affect x86 for now.
>>
>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>
> I think it's best to leave VFIO alone. Add appropriate APIs for VDPA,
> worry about converting existing users later.



Just to make sure I understand, did you mean:

1) introduce another bridge for vDPA

or

2) only detect vDPA via bypass manager? (we can leave VFIO code as is, 
then the assigned device counter may increase/decrease twice if VFIO use 
irq bypass manager which should be no harm).

Thanks


>
>> ---
>>   arch/x86/kvm/x86.c | 10 ++++++++--
>>   virt/kvm/vfio.c    |  2 --
>>   2 files changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 00c88c2..20c07d3 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -10624,11 +10624,17 @@ int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,
>>   {
>>   	struct kvm_kernel_irqfd *irqfd =
>>   		container_of(cons, struct kvm_kernel_irqfd, consumer);
>> +	int ret;
>>   
>>   	irqfd->producer = prod;
>> +	kvm_arch_start_assignment(irqfd->kvm);
>> +	ret = kvm_x86_ops.update_pi_irte(irqfd->kvm,
>> +					 prod->irq, irqfd->gsi, 1);
>> +
>> +	if (ret)
>> +		kvm_arch_end_assignment(irqfd->kvm);
>>   
>> -	return kvm_x86_ops.update_pi_irte(irqfd->kvm,
>> -					   prod->irq, irqfd->gsi, 1);
>> +	return ret;
>>   }
>>   
>>   void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
>> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
>> index 8fcbc50..111da52 100644
>> --- a/virt/kvm/vfio.c
>> +++ b/virt/kvm/vfio.c
>> @@ -226,7 +226,6 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>   		list_add_tail(&kvg->node, &kv->group_list);
>>   		kvg->vfio_group = vfio_group;
>>   
>> -		kvm_arch_start_assignment(dev->kvm);
>>   
>>   		mutex_unlock(&kv->lock);
>>   
>> @@ -254,7 +253,6 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>   				continue;
>>   
>>   			list_del(&kvg->node);
>> -			kvm_arch_end_assignment(dev->kvm);
>>   #ifdef CONFIG_SPAPR_TCE_IOMMU
>>   			kvm_spapr_tce_release_vfio_group(dev->kvm,
>>   							 kvg->vfio_group);
>> -- 
>> 1.8.3.1