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

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Message-ID: <447f47fa-32dd-a408-dd81-13a9839e0748@redhat.com>
Date:   Mon, 15 Oct 2018 10:22:33 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Tiwei Bie <tiwei.bie@...el.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        wexu@...hat.com, jfreimann@...hat.com, maxime.coquelin@...hat.com
Subject: 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:
>> 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;
>> [...]