Re: [PATCH net-next V2 6/8] vhost: packed ring support

[Jason Wang]

On 2018/10/15 äå6:25, Michael S. Tsirkin wrote:
> On Mon, Oct 15, 2018 at 10:51:06AM +0800, Jason Wang wrote:
> > On 2018å10æ15æ 10:43, Michael S. Tsirkin wrote:
> > > On Mon, Oct 15, 2018 at 10:22:33AM +0800, Jason Wang wrote:
> > > > On 2018å10æ13æ 01:23, Michael S. Tsirkin wrote:
> > > > > 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.
> > > > Ok, I assumes packed virtqueue support 64K but looks not. I can change it to
> > > > bit 15 and GET_VRING_BASE need to be changed as well.
> > > >
> > > > > > 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.
> > > > Do we need to clarify this in the spec?
> > > Isn't this all internal vhost stuff?
> > I meant the illegal index 0x8000-0xffff.
> It does say packed virtqueues support up to 2 15 entries each.
>
> But yes we can add a requirement that devices do not expose
> larger rings. Split does not support 2**16 either, right?
> With 2**16 enties avail index becomes 0 and ring looks empty.

Yes, so it's better to clarify this in the spec.

Thanks