Re: [Qemu-devel] commit virtio: recalculate vq->inuse after migration might cause last_avail_idx vs. used_idx failure

[Halil Pasic]

On 12/15/2016 11:52 AM, Dr. David Alan Gilbert wrote:
>> We got a bugreport with this log for a live migration target. 
>>
>> 2016-12-13T18:59:03.647309Z qemu-system-s390x: VQ 1 size 0x100 < 
>> last_avail_idx 0x2f76 - used_idx 0x762f
> Is this actually an endian problem - 2f76 vs 762f ?
> 
> Dave
> 

Thanks! It seems you are right:

static inline uint16_t vring_avail_idx(VirtQueue *vq)
{
    hwaddr pa;
    pa = vq->vring.avail + offsetof(VRingAvail, idx);
    vq->shadow_avail_idx = virtio_lduw_phys(vq->vdev, pa);

we should have an endiannes handling here before assigning shadow_avail_idx I 
guess

    return vq->shadow_avail_idx;
} 

I will meditate a bit more on this and probably create a patch to fix it.

What make me wonder is that according to the reports live migration usually
works (ca 1% fails)...

Can I credit you as reporter in case I end up making a fix?

Halil