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

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Message-ID: <ef510c97-1f1c-a121-99db-b659a5f9518c@intel.com>
Date:   Wed, 28 Apr 2021 17:56:02 +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 5:21 PM, Jason Wang wrote:
>
> 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.
when calling this, I think it targets a usersapce program, why kernel 
space need it, so IMHO no harm if we check this to keep the parent 
driver robust.
>
>
>>> 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.
If it is not page aligned, there would be extra complexities for 
vhost/qemu, I see it as a hardware defect, why adapt to this kind of 
defects?

Thanks
Zhu Lingshan
>
> 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)
>>>
>>
>