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

[Paolo Bonzini <pbonzini@redhat.com>]

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

> Moreover, is it feasible to skip the vhost_virtqueue_start() call for the unused
> queues in vhost_dev_start() in QEMU?
> 
> 
> 
> Thanks,
> Xiang
> 
>