Re: [PATCH] virtio_ring: add an error code check in virtqueue_resize

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Su Hui <suhui@nfschina.com>
Subject: Re: [PATCH] virtio_ring: add an error code check in virtqueue_resize
Date: Mon, 23 Oct 2023 07:18:38 -0400	[thread overview]
Message-ID: <20231023071752-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <1698058354.8316164-2-xuanzhuo@linux.alibaba.com>

On Mon, Oct 23, 2023 at 06:52:34PM +0800, Xuan Zhuo wrote:
> On Mon, 23 Oct 2023 17:52:02 +0800, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > On Mon, 23 Oct 2023 17:50:46 +0800, Su Hui <suhui@nfschina.com> wrote:
> > > On 2023/10/23 13:46, Xuan Zhuo wrote:
> > > >>>>>>>> Well, what are the cases where it can happen practically?
> > > >>>>>>> Device error. Such as vp_active_vq()
> > > >>>>>>>
> > > >>>>>>> Thanks.
> > > >>>>>> Hmm interesting. OK. But do callers know to recover?
> > > >>>>> No.
> > > >>>>>
> > > >>>>> So I think WARN + broken is suitable.
> > > >>>>>
> > > >>>>> Thanks.
> > > >>>> Sorry for the late, is the following code okay?
> > > >>>>
> > > >>>> @@ -2739,7 +2739,7 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num,
> > > >>>>                         void (*recycle)(struct virtqueue *vq, void *buf))
> > > >>>>     {
> > > >>>>            struct vring_virtqueue *vq = to_vvq(_vq);
> > > >>>> -       int err;
> > > >>>> +       int err, err_reset;
> > > >>>>
> > > >>>>            if (num > vq->vq.num_max)
> > > >>>>                    return -E2BIG;
> > > >>>> @@ -2759,7 +2759,15 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num,
> > > >>>>            else
> > > >>>>                    err = virtqueue_resize_split(_vq, num);
> > > >>>>
> > > >>>> -       return virtqueue_enable_after_reset(_vq);
> > > >>>> +       err_reset = virtqueue_enable_after_reset(_vq);
> > > >>>> +
> > > >>>> +       if (err) {
> > > >>> No err.
> > > >>>
> > > >>> err is not important.
> > > >>> You can remove that.
> > > >> Emm, I'm a little confused that which code should I remove ?
> > > >>
> > > >>
> > > >> like this:
> > > >> 	if (vq->packed_ring)
> > > >> 		virtqueue_resize_packed(_vq, num);
> > > >> 	else
> > > >> 		virtqueue_resize_split(_vq, num);
> > > >>
> > > >> And we should set broken and warn inside virtqueue_enable_after_reset()?
> > >
> > > In my opinion, we should return the error code of virtqueue_resize_packed() / virtqueue_resize_split().
> > > But if this err is not important, this patch makes no sense.
> > > Maybe I misunderstand somewhere...
> > > If you think it's worth sending a patch, you can send it :).(I'm not familiar with this code).
> >
> > OK.
> 
> Hi Michael,
> 
> The queue reset code is wrote with the CONFIG_VIRTIO_HARDEN_NOTIFICATION.
> 
> When we disable the vq, the broken is true until we re-enable it.
> 
> So when we re-enable it fail, the vq is broken status.
> 
> Normally, this just happens on the buggy device.
> So I think that is enough.
> 
> Thanks.

I don't know what to do about CONFIG_VIRTIO_HARDEN_NOTIFICATION.
It's known to be broken and it does not look like there's
active effort to revive it - should we just drop it for now?

> 
> 	static int vp_modern_disable_vq_and_reset(struct virtqueue *vq)
> 	{
> 		[...]
> 
> 		vp_modern_set_queue_reset(mdev, vq->index);
> 
> 		[...]
> 
> 	#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> ->>		__virtqueue_break(vq);
> 	#endif
> 
> 		[...]
> 	}
> 
> 	static int vp_modern_enable_vq_after_reset(struct virtqueue *vq)
> 	{
> 		[...]
> 
> 		if (vp_modern_get_queue_reset(mdev, index))
> 			return -EBUSY;
> 
> 		if (vp_modern_get_queue_enable(mdev, index))
> 			return -EBUSY;
> 
> 		err = vp_active_vq(vq, info->msix_vector);
> 		if (err)
> 			return err;
> 
> 		}
> 
> 		[...]
> 
> 	#ifdef CONFIG_VIRTIO_HARDEN_NOTIFICATION
> ->>		__virtqueue_unbreak(vq);
> 	#endif
> 
> 		[...]
> 	}
> 
> 
> 
> 
> >
> > Thanks.
> >
> >
> > >
> > > Thanks,
> > > Su Hui
> > >