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

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Date:   Wed, 28 Apr 2021 17:21:48 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.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


在 2021/4/28 下午4:59, Zhu, Lingshan 写道:
>
>
> 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.


The point is parent is unaware of whether or not there's a userspace.


>> 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.


Typo, what I meant is "it can't be used". That is to say, we should let 
the vDPA bus driver to decide whether or not it can be used.

Thanks


>
> 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)
>>
>