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    SubjectRe: [PATCH 5/6] vdpa: add get_vq_num_unchangeable callback in vdpa_config_ops
    On Thu, Sep 09, 2021 at 05:28:26PM +0800, Jason Wang wrote:
    > 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
    I agree, it is a good idea.
    BTW, can we also advertise mac address of network device? I found the
    mac address generated by libvirt or qemu will break the network datapath
    down if I don't specify the right mac explicitly in the XML or qemu
    commandline.
    >
    > >
    > > 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
    > > > >
    > >

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