Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: kpadCj3J+AsXrGk2mCT/D00zqIf/qgoNS0WDNvteuL89SLv8N9QyDs/lSqvEepLXSnCTrImKZw
 8hQwxNI2QuzA==
IronPort-SDR: dApj3T9INT2w9mW71TQIAdeviU5ltiqx14WUEmw+LwjnFS3O4jIxFpuC/Hd1E4va7S6f4Z9qIy
 FcX79hJFbAMQ==
Subject: Re: [PATCH 2/2] vDPA/ifcvf: implement doorbell mapping for ifcvf
To:     Jason Wang <jasowang@redhat.com>, mst@redhat.com
Cc:     virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210428082133.6766-1-lingshan.zhu@intel.com>
 <20210428082133.6766-3-lingshan.zhu@intel.com>
 <f6d9a424-9025-3eb5-1cb4-0ff22f7bec63@redhat.com>
 <5052fced-cd9a-e453-5cb2-39cdde60a208@intel.com>
 <1984491f-cd5e-d4bc-b328-41e2f2e935fd@redhat.com>
 <ef510c97-1f1c-a121-99db-b659a5f9518c@intel.com>
 <4e0eda74-04ac-a889-471b-03fe65c65606@redhat.com>
From:   "Zhu, Lingshan" <lingshan.zhu@intel.com>
Message-ID: <f4cb4619-5634-e42d-0629-5c40f6b0dcd1@intel.com>
Date:   Wed, 28 Apr 2021 18:20:10 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.9.0
MIME-Version: 1.0
In-Reply-To: <4e0eda74-04ac-a889-471b-03fe65c65606@redhat.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk


On 4/28/2021 6:03 PM, Jason Wang wrote:
>
> 在 2021/4/28 下午5:56, Zhu, Lingshan 写道:
>>
>>
>> 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@intel.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.
>
>
> Again, vDPA device is unaware of what driver that is bound. It could 
> be virtio-vpda, vhost-vdpa or other in the future. It's only the vDPA 
> bus driver know how it is actually used.
>
>
>>>
>>>
>>>>> 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, 
>
>
> It is allowed by the virtio spec, isn't it?
The spec does not require the doorbell to be page size aligned, however 
it still a hardware defect if non page size aligned notify base present, 
I will leave a warning message here instead of the 0 value.

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