Re: [PATCH RFC 09/15] hw/virtio/vhost-shadow-virtqueue: specified vring placement

On 2026/08/07 0:29, Connor Kite wrote:
> On Fri, Jul 24, 2026 at 5:19 AM Akihiko Odaki
> <[email protected]> wrote:
> ...
>>
>> Nit: please remove the whitespace between (void *) and svq->base_addr.
>>
> 
> Removing the whitespace!
> 
>>> +        svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size);
>>> +        svq->vring.used = (void *)((char *)svq->base_addr +
>>> +                          vhost_svq_driver_area_size(svq));
>>> +    }
>>
>> Unmapping svq here can lead to use-after-unmapping because the ring is
>> not stopped yet. do_vhost_dev_stop() calls do_vhost_virtqueue_stop()
>> only after calling hdev->vhost_ops->vhost_dev_start(hdev, false).
>>
> 
> I am afraid I don't quite understand, as this patch does not introduce
> any unmapping.
> Was this comment meant for a different patch?

Yes, sorry, this comment was meant for "[PATCH RFC 14/15] 
hw/virtio/vhost-user: handle data movement with shadow vqs".

vhost_user_dev_start(dev, false) calls vhost_user_svqs_stop(), which 
calls vhost_svq_stop() and unmaps the shadow vring. However, 
do_vhost_dev_stop() calls do_vhost_virtqueue_stop() only after the 
callback returns. The backend vring therefore remains active until 
VHOST_USER_GET_VRING_BASE, so it may still access the unmapped memory.

Regards,
Akihiko Odaki