linux-kernel - Re: [PATCH 2/2] vDPA/ifcvf: implement doorbell mapping for ifcvf

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Date:   Wed, 28 Apr 2021 16:59:26 +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, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] vDPA/ifcvf: implement doorbell mapping for ifcvf



On 4/28/2021 4:42 PM, Jason Wang wrote:
>
> 在 2021/4/28 下午4:21, 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 | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c 
>> b/drivers/vdpa/ifcvf/ifcvf_main.c
>> index e48e6b74fe2e..afcb71bc0f51 100644
>> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
>> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
>> @@ -413,6 +413,23 @@ 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_hw *vf = vdpa_to_vf(vdpa_dev);
>> +    struct vdpa_notification_area area;
>> +
>> +    if (vf->notify_pa % PAGE_SIZE) {
>> +        area.addr = 0;
>> +        area.size = 0;
>
>
> We don't need this since:
>
> 1) there's a check in the vhost vDPA
I think you mean this code block in vdpa.c
         notify = ops->get_vq_notification(vdpa, index);
         if (notify.addr & (PAGE_SIZE - 1))
                 return -EINVAL;

This should work, however, I think the parent driver should ensure it 
passes a PAGE_SIZE aligned address to userspace, to be robust, to be 
reliable.
> 2) device is unaware of the bound driver, non page aligned doorbell 
> doesn't necessarily meant it can be used
Yes, non page aligned doorbell can not be used, so there is a check.

Thanks
Zhu Lingshan
>
> Let's leave those polices to the driver.
>
> Thanks
>
>
>> +    } else {
>> +        area.addr = vf->notify_pa;
>> +        area.size = PAGE_SIZE;
>> +    }
>> +
>> +    return area;
>> +}
>> +
>>   /*
>>    * IFCVF currently does't have on-chip IOMMU, so not
>>    * implemented set_map()/dma_map()/dma_unmap()
>> @@ -440,6 +457,7 @@ 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)
>