netdev - Re: [PATCH v5] vhost: introduce mdev based hardware backend

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Date:   Thu, 7 Nov 2019 13:27:05 +0800
From:   Tiwei Bie <tiwei.bie@...el.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, alex.williamson@...hat.com,
        maxime.coquelin@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, dan.daly@...el.com,
        cunming.liang@...el.com, zhihong.wang@...el.com,
        lingshan.zhu@...el.com
Subject: Re: [PATCH v5] vhost: introduce mdev based hardware backend

On Thu, Nov 07, 2019 at 12:08:08PM +0800, Jason Wang wrote:
> On 2019/11/6 下午10:49, Tiwei Bie wrote:
> > > > > > > +	default:
> > > > > > > +		/*
> > > > > > > +		 * VHOST_SET_MEM_TABLE, VHOST_SET_LOG_BASE, and
> > > > > > > +		 * VHOST_SET_LOG_FD are not used yet.
> > > > > > > +		 */
> > > > > > If we don't even use them, there's probably no need to call
> > > > > > vhost_dev_ioctl(). This may help to avoid confusion when we want to develop
> > > > > > new API for e.g dirty page tracking.
> > > > > Good point. It's better to reject these ioctls for now.
> > > > > 
> > > > > PS. One thing I may need to clarify is that, we need the
> > > > > VHOST_SET_OWNER ioctl to get the vq->handle_kick to work.
> > > > > So if we don't call vhost_dev_ioctl(), we will need to
> > > > > call vhost_dev_set_owner() directly.
> > > I may miss something, it looks to me the there's no owner check in
> > > vhost_vring_ioctl() and the vhost_poll_start() can make sure handle_kick
> > > works?
> > Yeah, there is no owner check in vhost_vring_ioctl().
> > IIUC, vhost_poll_start() will start polling the file. And when
> > event arrives, vhost_poll_wakeup() will be called, and it will
> > queue work to work_list and wakeup worker to finish the work.
> > And the worker is created by vhost_dev_set_owner().
> > 
> 
> Right, rethink about this. It looks to me we need:
> 
> - Keep VHOST_SET_OWNER, this could be used for future control vq where it
> needs a kthread to access the userspace memory
> 
> - Temporarily filter  SET_LOG_BASE and SET_LOG_FD until we finalize the API
> for dirty page tracking.
> 
> - For kick through kthread, it looks sub-optimal but we can address this in
> the future, e.g call handle_vq_kick directly in vhost_poll_queue (probably a
> flag for vhost_poll) and deal with the synchronization in vhost_poll_flush
> carefully.

OK.

Thanks,
Tiwei

> 
> Thanks
> 
>