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SubjectRe: [PATCH net-next V2 6/8] vhost: packed ring support
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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:
>> 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?

>>> + 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

>>
>>> + 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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