Re: [PATCH v6 6/8] virtio_vdpa: setup correct vq size with callbacks get_vq_num_{max,min}

[Jason Wang]

在 2021/10/25 上午10:44, Wu Zongyong 写道:
> On Mon, Oct 25, 2021 at 10:22:30AM +0800, Jason Wang wrote:
> > On Fri, Oct 22, 2021 at 10:45 AM Wu Zongyong
> > <wuzongyong@xxxxxxxxxxxxxxxxx> wrote:
> > > For the devices which implement the get_vq_num_min callback, the driver
> > > should not negotiate with virtqueue size with the backend vdpa device if
> > > the value returned by get_vq_num_min equals to the value returned by
> > > get_vq_num_max.
> > > This is useful for vdpa devices based on legacy virtio specfication.
> > >
> > > Signed-off-by: Wu Zongyong <wuzongyong@xxxxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/virtio/virtio_vdpa.c | 21 ++++++++++++++++-----
> > >   1 file changed, 16 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> > > index 72eaef2caeb1..e42ace29daa1 100644
> > > --- a/drivers/virtio/virtio_vdpa.c
> > > +++ b/drivers/virtio/virtio_vdpa.c
> > > @@ -145,7 +145,8 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> > >          /* Assume split virtqueue, switch to packed if necessary */
> > >          struct vdpa_vq_state state = {0};
> > >          unsigned long flags;
> > > -       u32 align, num;
> > > +       u32 align, max_num, min_num = 0;
> > > +       bool may_reduce_num = true;
> > >          int err;
> > >
> > >          if (!name)
> > > @@ -163,22 +164,32 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> > >          if (!info)
> > >                  return ERR_PTR(-ENOMEM);
> > >
> > > -       num = ops->get_vq_num_max(vdpa);
> > > -       if (num == 0) {
> > > +       max_num = ops->get_vq_num_max(vdpa);
> > > +       if (max_num == 0) {
> > >                  err = -ENOENT;
> > >                  goto error_new_virtqueue;
> > >          }
> > >
> > > +       if (ops->get_vq_num_min)
> > > +               min_num = ops->get_vq_num_min(vdpa);
> > > +
> > > +       may_reduce_num = (max_num == min_num) ? false : true;
> > > +
> > >          /* Create the vring */
> > >          align = ops->get_vq_align(vdpa);
> > > -       vq = vring_create_virtqueue(index, num, align, vdev,
> > > -                                   true, true, ctx,
> > > +       vq = vring_create_virtqueue(index, max_num, align, vdev,
> > > +                                   true, may_reduce_num, ctx,
> > >                                      virtio_vdpa_notify, callback, name);
> > >          if (!vq) {
> > >                  err = -ENOMEM;
> > >                  goto error_new_virtqueue;
> > >          }
> > >
> > > +       if (virtqueue_get_vring_size(vq) < min_num) {
> > > +               err = -EINVAL;
> > > +               goto err_vq;
> > > +       }
> > I wonder under which case can we hit this?
> >
> > Thanks
> If min_vq_num < max_vq_num, may_reduce_num should be true, then it is
> possible to allocate a virtqueue with a small size which value is less
> than the min_vq_num since we only set the upper bound for virtqueue size
> when creating virtqueue.
>
> Refers to vring_create_virtqueue_split in driver/virtio/virtio_vring.c:
>
> 	for (; num && vring_size(num, vring_align) > PAGE_SIZE; num /= 2) {
> 		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
> 					  &dma_addr,
> 					  GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
> 		if (queue)
> 			break;
> 		if (!may_reduce_num)
> 			return NULL;
> 	}


It looks to me it's better to fix this function instead of checking it 
in the caller?


> BTW, I have replied this mail on Nov.18, have you ever received it?


For some reason I dont' get that.

Thanks


> > > +
> > >          /* Setup virtqueue callback */
> > >          cb.callback = virtio_vdpa_virtqueue_cb;
> > >          cb.private = info;
> > > --
> > > 2.31.1