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Subject: Re: [RFC V4 PATCH 7/8] vhost: packed ring support
To:     Wei Xu <wexu@redhat.com>
Cc:     mst@redhat.com, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, jfreimann@redhat.com,
        tiwei.bie@intel.com
References: <1526473941-16199-1-git-send-email-jasowang@redhat.com>
 <1526473941-16199-8-git-send-email-jasowang@redhat.com>
 <20180522165448.GA13523@wei-ubt>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <e12d4055-6ae6-4d00-ae8b-1acd88633f48@redhat.com>
Date:   Wed, 23 May 2018 09:39:28 +0800
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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@redhat.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.

Thanks