Re: [PATCH] OvmfPkg/VirtioScsiDxe: Allocate all required vrings at VirtioScsiInit

["zhengxiang (A)" <zhengxiang9@huawei.com>]

Hi Maxime,

On 2018/1/11 22:46, Maxime Coquelin wrote:
> 
> 
> On 01/11/2018 02:23 PM, Maxime Coquelin wrote:
>> Hi Xiang,
>>
>> On 12/14/2017 02:25 PM, zhengxiang (A) wrote:
>>>
>>>
>>> On 2017/12/14 17:06, Paolo Bonzini wrote:
>>>> On 14/12/2017 07:55, zhengxiang (A) wrote:
>>>>> Hello Laszlo and Paolo,
>>>>>
>>>>> Thanks for your review!
>>>>>
>>>>> On 2017/12/13 19:16, Laszlo Ersek wrote:
>>>>>> On 12/13/17 10:29, Paolo Bonzini wrote:
>>>>>>> On 13/12/2017 09:35, Laszlo Ersek wrote:
>>>>>>>> Perhaps you can update vhost-scsi similarly to the last patch of
>>>>>>>> Maxime's v4 series, even without "VIRTIO_SCSI_F_MQ" -- in the
>>>>>>>> SET_FEATURES request handler, just destroy the unused virtqueues that
>>>>>>>> have not been configured by the guest driver until that time?
>>>>>>> Yes, this is the right solution.  We can assume that if the descriptor
>>>>>>> address is equal to zero, the queue is not in use.  This is not in the
>>>>>>> spec as far as I can see, but it is QEMU's assumption.  I will send a
>>>>>>> patch to the virtio specification.
>>>>>
>>>>> I would try this solution! However, is there any possibility that the allocated
>>>>> descriptor address is exactly equal to zero and the queue is in use?
>>>>
>>>> That would break QEMU's virtio implementation, so it's pretty unlikely.
>>>>
>>>> Paolo
>>>>
>>>
>>> So could I judge the not-in-use queues by adding the below sentence in order
>>> to skip calling vhost_virtqueue_start?
>>>
>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>>> index e4290ce..05c3322 100644
>>> --- a/hw/virtio/vhost.c
>>> +++ b/hw/virtio/vhost.c
>>> @@ -1532,6 +1532,7 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
>>>           goto fail_mem;
>>>       }
>>>       for (i = 0; i < hdev->nvqs; ++i) {
>>> +        if (virtio_queue_get_desc_addr(vdev, i) == 0) continue;
> 
> BTW, the queue index is wrong here, it should be:
> 
> if (virtio_queue_get_desc_addr(vdev, hdev->vq_index + i) == 0)
>     continue;
> 
Thank you for correcting my mistake. I will post this patch for more discussions.
>>>           r = vhost_virtqueue_start(hdev,
>>>                                     vdev,
>>>                                     hdev->vqs + i,
>>>
>>
> 
> Maxime
> 
> .
> 

Thanks,
Xiang