Hi Jason & Michael, Do you have any idea about this problem ?
-- Regards, Longpeng(Mike) On 2017/11/15 23:54, Longpeng(Mike) wrote: > 2017-11-15 23:05 GMT+08:00 Jason Wang <jasow...@redhat.com>: >> >> >> On 2017年11月15日 22:55, Longpeng(Mike) wrote: >>> >>> Hi guys, >>> >>> We got a BUG report from our testers yesterday, the testing scenario was >>> migrating a VM (Windows guest, *4 vcpus*, 4GB, vhost-user net: *7 >>> queues*). >>> >>> We found the cause reason, and we'll report the BUG or send a fix patch >>> to upstream if necessary( we haven't test the upstream yet, sorry... ). >> >> >> Could you explain this a little bit more? >> >>> >>> We want to know why the vhost_net_start() must start *total queues* ( in >>> our >>> VM there're 7 queues ) but not *the queues that current used* ( in our VM, >>> guest >>> only uses the first 4 queues because it's limited by the number of vcpus) >>> ? >>> >>> Looking forward to your help, thx :) >> >> >> Since the codes have been there for years and works well for kernel >> datapath. You should really explain what's wrong. >> > > OK. :) > > In our scenario, the Windows's virtio-net driver only use the first 4 > queues and it > *only set desc/avail/used table for the first 4 queues*, so in QEMU > the desc/avail/ > used of the last 3 queues are ZERO, but unfortunately... > ''' > vhost_net_start > for (i = 0; i < total_queues; i++) > vhost_net_start_one > vhost_dev_start > vhost_virtqueue_start > ''' > In vhost_virtqueue_start(), it will calculate the HVA of > desc/avail/used table, so for last > 3 queues, it will use ZERO as the GPA to calculate the HVA, and then > send the results > to the user-mode backend ( we use *vhost-user* ) by > vhost_virtqueue_set_addr(). > > When the EVS get these address, it will update a *idx* which will be > treated as vq's > last_avail_idx when virtio-net stop ( pls see vhost_virtqueue_stop() ). > > So we get the following result after virtio-net stop: > the desc/avail/used of the last 3 queues's vqs are all ZERO, but these vqs's > last_avail_idx is NOT ZERO. > > At last, virtio_load() reports an error: > ''' > if (!vdev->vq[i].vring.desc && vdev->vq[i].last_avail_idx) { // <-- > will be TRUE > error_report("VQ %d address 0x0 " > "inconsistent with Host index 0x%x", > i, vdev->vq[i].last_avail_idx); > return -1; > } > ''' > > BTW, the problem won't appear if use Linux guest, because the Linux virtio-net > driver will set all 7 queues's desc/avail/used tables. And the problem > won't appear > if the VM use vhost-net, because vhost-net won't update *idx* in SET_ADDR > ioctl. > > Sorry for my pool English, Maybe I could describe the problem in Chinese for > you > in private if necessary. > > >> Thanks > > -- Regards, Longpeng(Mike)