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From:   Jason Wang <jasowang@redhat.com>
Date:   Thu, 9 Sep 2021 17:28:26 +0800
Message-ID: <CACGkMEsnp7-axbZWuB_w7ZkSWKa0Y+Ej-Kq0QSfO2-DNN=ShVA@mail.gmail.com>
Subject: Re: [PATCH 5/6] vdpa: add get_vq_num_unchangeable callback in vdpa_config_ops
To:     Wu Zongyong <wuzongyong@linux.alibaba.com>
Cc:     virtualization <virtualization@lists.linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        mst <mst@redhat.com>, wei.yang1@linux.alibaba.com
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On Thu, Sep 9, 2021 at 4:02 PM Wu Zongyong <wuzongyong@linux.alibaba.com> wrote:
>
> On Thu, Sep 09, 2021 at 10:55:03AM +0800, Jason Wang wrote:
> > On Wed, Sep 8, 2021 at 8:23 PM Wu Zongyong <wuzongyong@linux.alibaba.com> wrote:
> > >
> > > This new callback is used to indicate whether the vring size can be
> > > change or not. It is useful when we have a legacy virtio pci device as
> > > the vdpa device for there is no way to negotiate the vring num by the
> > > specification.
> >
> > So I'm not sure it's worth bothering. E.g what if we just fail
> > VHOST_SET_VRING_NUM it the value doesn't match what hardware has?
> >
> > Thanks
> >
> I think we should not call VHOST_SET_VRING_NUM in that case.
>
> If the hardware reports that the virtqueue size cannot be changed, we
> should call VHOST_GET_VRING_NUM to get the static virtqueue size
> firstly, then allocate the same size memory for the virtqueues and write
> the address to hardware finally.
>
> For QEMU, we will ignore the properties rx/tx_queue_size and just get it
> from the hardware if this new callback return true.

This will break live migration. My understanding is that we can
advertise those capability/limitation via the netlink management
protocol then management layer can choose to use the correct queue
size.

Thanks

>
> What do you think?
> > >
> > > Signed-off-by: Wu Zongyong <wuzongyong@linux.alibaba.com>
> > > ---
> > >  drivers/vhost/vdpa.c         | 19 +++++++++++++++++++
> > >  drivers/virtio/virtio_vdpa.c |  5 ++++-
> > >  include/linux/vdpa.h         |  4 ++++
> > >  include/uapi/linux/vhost.h   |  2 ++
> > >  4 files changed, 29 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > > index 9479f7f79217..2204d27d1e5d 100644
> > > --- a/drivers/vhost/vdpa.c
> > > +++ b/drivers/vhost/vdpa.c
> > > @@ -350,6 +350,22 @@ static long vhost_vdpa_get_iova_range(struct vhost_vdpa *v, u32 __user *argp)
> > >         return 0;
> > >  }
> > >
> > > +static long vhost_vdpa_get_vring_num_unchangeable(struct vhost_vdpa *v,
> > > +                                                 u32 __user *argp)
> > > +{
> > > +       struct vdpa_device *vdpa = v->vdpa;
> > > +       const struct vdpa_config_ops *ops = vdpa->config;
> > > +       bool unchangeable = false;
> > > +
> > > +       if (ops->get_vq_num_unchangeable)
> > > +               unchangeable = ops->get_vq_num_unchangeable(vdpa);
> > > +
> > > +       if (copy_to_user(argp, &unchangeable, sizeof(unchangeable)))
> > > +               return -EFAULT;
> > > +
> > > +       return 0;
> > > +}
> > > +
> > >  static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
> > >                                    void __user *argp)
> > >  {
> > > @@ -487,6 +503,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> > >         case VHOST_VDPA_GET_IOVA_RANGE:
> > >                 r = vhost_vdpa_get_iova_range(v, argp);
> > >                 break;
> > > +       case VHOST_VDPA_GET_VRING_NUM_UNCHANGEABLE:
> > > +               r = vhost_vdpa_get_vring_num_unchangeable(v, argp);
> > > +               break;
> > >         default:
> > >                 r = vhost_dev_ioctl(&v->vdev, cmd, argp);
> > >                 if (r == -ENOIOCTLCMD)
> > > diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> > > index 72eaef2caeb1..afb47465307a 100644
> > > --- a/drivers/virtio/virtio_vdpa.c
> > > +++ b/drivers/virtio/virtio_vdpa.c
> > > @@ -146,6 +146,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> > >         struct vdpa_vq_state state = {0};
> > >         unsigned long flags;
> > >         u32 align, num;
> > > +       bool may_reduce_num = true;
> > >         int err;
> > >
> > >         if (!name)
> > > @@ -171,8 +172,10 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
> > >
> > >         /* Create the vring */
> > >         align = ops->get_vq_align(vdpa);
> > > +       if (ops->get_vq_num_unchangeable)
> > > +               may_reduce_num = !ops->get_vq_num_unchangeable(vdpa);
> > >         vq = vring_create_virtqueue(index, num, align, vdev,
> > > -                                   true, true, ctx,
> > > +                                   true, may_reduce_num, ctx,
> > >                                     virtio_vdpa_notify, callback, name);
> > >         if (!vq) {
> > >                 err = -ENOMEM;
> > > diff --git a/include/linux/vdpa.h b/include/linux/vdpa.h
> > > index 35648c11e312..f809b7ada00d 100644
> > > --- a/include/linux/vdpa.h
> > > +++ b/include/linux/vdpa.h
> > > @@ -195,6 +195,9 @@ struct vdpa_iova_range {
> > >   *                             @vdev: vdpa device
> > >   *                             Returns the iova range supported by
> > >   *                             the device.
> > > + * @get_vq_num_unchangeable    Check if size of virtqueue is unchangeable (optional)
> > > + *                             @vdev: vdpa device
> > > + *                             Returns boolean: unchangeable (true) or not (false)
> > >   * @set_map:                   Set device memory mapping (optional)
> > >   *                             Needed for device that using device
> > >   *                             specific DMA translation (on-chip IOMMU)
> > > @@ -262,6 +265,7 @@ struct vdpa_config_ops {
> > >                            const void *buf, unsigned int len);
> > >         u32 (*get_generation)(struct vdpa_device *vdev);
> > >         struct vdpa_iova_range (*get_iova_range)(struct vdpa_device *vdev);
> > > +       bool (*get_vq_num_unchangeable)(struct vdpa_device *vdev);
> > >
> > >         /* DMA ops */
> > >         int (*set_map)(struct vdpa_device *vdev, struct vhost_iotlb *iotlb);
> > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> > > index c998860d7bbc..184f1f7f8498 100644
> > > --- a/include/uapi/linux/vhost.h
> > > +++ b/include/uapi/linux/vhost.h
> > > @@ -150,4 +150,6 @@
> > >  /* Get the valid iova range */
> > >  #define VHOST_VDPA_GET_IOVA_RANGE      _IOR(VHOST_VIRTIO, 0x78, \
> > >                                              struct vhost_vdpa_iova_range)
> > > +/* Check if the vring size can be change */
> > > +#define VHOST_VDPA_GET_VRING_NUM_UNCHANGEABLE _IOR(VHOST_VIRTIO, 0X79, bool)
> > >  #endif
> > > --
> > > 2.31.1
> > >
>