netdev - Re: [PATCH V2 RESEND 2/2] vDPA/ifcvf: implement doorbell mapping for ifcvf

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Date:   Tue, 1 Jun 2021 11:27:43 +0800
From:   "Zhu, Lingshan" <lingshan.zhu@...el.com>
To:     Jason Wang <jasowang@...hat.com>, mst@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH V2 RESEND 2/2] vDPA/ifcvf: implement doorbell mapping for
 ifcvf



On 5/31/2021 3:56 PM, Jason Wang wrote:
>
> 在 2021/5/31 下午3:33, Zhu Lingshan 写道:
>> This commit implements doorbell mapping feature for ifcvf.
>> This feature maps the notify page to userspace, to eliminate
>> vmexit when kick a vq.
>>
>> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
>> ---
>>   drivers/vdpa/ifcvf/ifcvf_main.c | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
>>
>> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c 
>> b/drivers/vdpa/ifcvf/ifcvf_main.c
>> index ab0ab5cf0f6e..effb0e549135 100644
>> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
>> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
>> @@ -413,6 +413,22 @@ static int ifcvf_vdpa_get_vq_irq(struct 
>> vdpa_device *vdpa_dev,
>>       return vf->vring[qid].irq;
>>   }
>>   +static struct vdpa_notification_area 
>> ifcvf_get_vq_notification(struct vdpa_device *vdpa_dev,
>> +                                   u16 idx)
>> +{
>> +    struct ifcvf_adapter *adapter = vdpa_to_adapter(vdpa_dev);
>> +    struct ifcvf_hw *vf = vdpa_to_vf(vdpa_dev);
>> +    struct pci_dev *pdev = adapter->pdev;
>> +    struct vdpa_notification_area area;
>> +
>> +    area.addr = vf->vring[idx].notify_pa;
>> +    area.size = PAGE_SIZE;
>> +    if (area.addr % PAGE_SIZE)
>> +        IFCVF_DBG(pdev, "vq %u doorbell address is not PAGE_SIZE 
>> aligned\n", idx);
>
>
> Let's leave the decision to upper layer by: (see 
> vp_vdpa_get_vq_notification)
>
> area.addr = notify_pa;
> area.size = notify_offset_multiplier;
>
> Thanks

Hi Jason,

notify_offset_multiplier can be zero, means vqs share the same doorbell 
address, distinguished by qid.
and in vdpa.c:

         if (vma->vm_end - vma->vm_start != notify.size)
                 return -ENOTSUPP;

so a zero size would cause this feature failure.
mmap should work on at least a page, so if we really want "area.size = 
notify_offset_multiplier;"
I think we should add some code in vdpa.c, like:

if(!notify.size)
     notify.size = PAGE_SIZE;

sounds good?

Thanks
Zhu Lingshan
>
>
>> +
>> +    return area;
>> +}
>> +
>>   /*
>>    * IFCVF currently does't have on-chip IOMMU, so not
>>    * implemented set_map()/dma_map()/dma_unmap()
>> @@ -440,6 +456,7 @@ static const struct vdpa_config_ops ifc_vdpa_ops = {
>>       .get_config    = ifcvf_vdpa_get_config,
>>       .set_config    = ifcvf_vdpa_set_config,
>>       .set_config_cb  = ifcvf_vdpa_set_config_cb,
>> +    .get_vq_notification = ifcvf_get_vq_notification,
>>   };
>>     static int ifcvf_probe(struct pci_dev *pdev, const struct 
>> pci_device_id *id)
>