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SubjectRe: [PATCH net-next V2 6/8] vhost: packed ring support
On Fri, Oct 12, 2018 at 10:32:44PM +0800, Tiwei Bie wrote:
> On Mon, Jul 16, 2018 at 11:28:09AM +0800, Jason Wang wrote:
> [...]
> > @@ -1367,10 +1397,48 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
> > vq->last_avail_idx = s.num;
> > /* Forget the cached index value. */
> > vq->avail_idx = vq->last_avail_idx;
> > + if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
> > + vq->last_avail_wrap_counter = wrap_counter;
> > + vq->avail_wrap_counter = vq->last_avail_wrap_counter;
> > + }
> > break;
> > case VHOST_GET_VRING_BASE:
> > s.index = idx;
> > s.num = vq->last_avail_idx;
> > + if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> > + s.num |= vq->last_avail_wrap_counter << 31;
> > + if (copy_to_user(argp, &s, sizeof(s)))
> > + r = -EFAULT;
> > + break;
> > + case VHOST_SET_VRING_USED_BASE:
> > + /* Moving base with an active backend?
> > + * You don't want to do that.
> > + */
> > + if (vq->private_data) {
> > + r = -EBUSY;
> > + break;
> > + }
> > + if (copy_from_user(&s, argp, sizeof(s))) {
> > + r = -EFAULT;
> > + break;
> > + }
> > + if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
> > + wrap_counter = s.num >> 31;
> > + s.num &= ~(1 << 31);
> > + }
> > + if (s.num > 0xffff) {
> > + r = -EINVAL;
> > + break;
> > + }
>
> Do we want to put wrap_counter at bit 15?

I think I second that - seems to be consistent with
e.g. event suppression structure and the proposed
extension to driver notifications.


> If put wrap_counter at bit 31, the check (s.num > 0xffff)
> won't be able to catch the illegal index 0x8000~0xffff for
> packed ring.
>
> > + vq->last_used_idx = s.num;
> > + if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> > + vq->last_used_wrap_counter = wrap_counter;
> > + break;
> > + case VHOST_GET_VRING_USED_BASE:
>
> Do we need the new VHOST_GET_VRING_USED_BASE and
> VHOST_SET_VRING_USED_BASE ops?
>
> We are going to merge below series in DPDK:
>
> http://patches.dpdk.org/patch/45874/
>
> We may need to reach an agreement first.
>
>
> > + s.index = idx;
> > + s.num = vq->last_used_idx;
> > + if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
> > + s.num |= vq->last_used_wrap_counter << 31;
> > if (copy_to_user(argp, &s, sizeof s))
> > r = -EFAULT;
> > break;
> [...]

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