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

On 2018/10/16 下午9:58, Maxime Coquelin wrote:

On 10/15/2018 04:22 AM, Jason Wang wrote:

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

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

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

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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?

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+        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.

I'm fine to put wrap_counter at bit 15.
I will post a new version of the DPDK series soon.

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

For split ring, we used to set the last_used_idx to the same value as
last_avail_idx as VHOST_USER_GET_VRING_BASE cannot be called while the
ring is being processed, so their value is always the same at the time
the request is handled.

I may miss something, but it looks to me we should sync last_used_idx 
from used_idx.

Thanks

I kept the same behavior for packed ring, and so the wrap counter have
to be the same.

Regards,
Maxime

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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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