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SubjectRe: [PATCH net-next V2 6/8] vhost: packed ring support
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On 2018/10/15 下午6:25, Michael S. Tsirkin wrote:
> On Mon, Oct 15, 2018 at 10:51:06AM +0800, Jason Wang wrote:
>> On 2018年10月15日 10:43, Michael S. Tsirkin wrote:
>>> On Mon, Oct 15, 2018 at 10:22:33AM +0800, Jason Wang wrote:
>>>> 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?
>>> 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


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