linux-kernel - Re: [RFC V4 PATCH 7/8] vhost: packed ring support

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Message-ID: <d2f9192f-9a4c-da35-72b5-c55df1efc01e@redhat.com>
Date:   Wed, 23 May 2018 16:57:46 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Wei Xu <wexu@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, jfreimann@...hat.com,
        tiwei.bie@...el.com
Subject: Re: [RFC V4 PATCH 7/8] vhost: packed ring support



On 2018年05月23日 15:17, Wei Xu wrote:
> On Wed, May 23, 2018 at 09:39:28AM +0800, Jason Wang wrote:
>>
>> On 2018年05月23日 00:54, Wei Xu wrote:
>>> On Wed, May 16, 2018 at 08:32:20PM +0800, Jason Wang wrote:
>>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>>>> ---
>>>>   drivers/vhost/net.c   |   3 +-
>>>>   drivers/vhost/vhost.c | 539 ++++++++++++++++++++++++++++++++++++++++++++++----
>>>>   drivers/vhost/vhost.h |   8 +-
>>>>   3 files changed, 513 insertions(+), 37 deletions(-)
>>>>
>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>>> index 8304c30..f2a0f5b 100644
>>>> --- a/drivers/vhost/vhost.c
>>>> +++ b/drivers/vhost/vhost.c
>>>> @@ -1358,6 +1382,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
>>>>   			break;
>>>>   		}
>>>>   		vq->last_avail_idx = s.num;
>>>> +		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
>>>> +			vq->avail_wrap_counter = s.num >> 31;
>>>>   		/* Forget the cached index value. */
>>>>   		vq->avail_idx = vq->last_avail_idx;
>>>>   		break;
>>>> @@ -1366,6 +1392,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
>>>>   		s.num = vq->last_avail_idx;
>>>>   		if (copy_to_user(argp, &s, sizeof s))
>>>>   			r = -EFAULT;
>>>> +		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
>>>> +			s.num |= vq->avail_wrap_counter << 31;
>>>>   		break;
>>>>   	case VHOST_SET_VRING_ADDR:
>>>>   		if (copy_from_user(&a, argp, sizeof a)) {
>>> 'last_used_idx' also needs to be saved/restored here.
>>>
>>> I have figured out the root cause of broken device after reloading
>>> 'virtio-net' module, all indices have been reset for a reloading but
>>> 'last_used_idx' is not properly reset in this case. This confuses
>>> handle_rx()/tx().
>>>
>>> Wei
>>>
>> Good catch, so we probably need a new ioctl to sync between qemu and vhost.
>>
>> Something like VHOST_SET/GET_USED_BASE.
> Sure, or can we expand 'vhost_vring_state' to keep them done in a bunch?

It's port of uapi, so we can't.

Thanks

>
>> Thanks
>>