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

On 2018年10月13日 01:23, Michael S. Tsirkin wrote:

On Fri, Oct 12, 2018 at 10:32:44PM +0800, Tiwei Bie wrote:

quoted

On Mon, Jul 16, 2018 at 11:28:09AM +0800, Jason Wang wrote:
[...]

quoted

@@ -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.

quoted

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?

quoted

quoted

+		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.

If we agree that 64K virtqueue won't be supported, I'm ok with either.

Btw the code assumes used_wrap_counter is equal to avail_wrap_counter 
which looks wrong?

Thanks

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+		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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