Re: [Qemu-devel] QEMU terminates during reboot after memory unplug with vhost=on

[Igor Mammedov]

On Thu, 14 Sep 2017 12:31:18 +0530
Bharata B Rao <address@hidden> wrote:

> Hi,
> 
> QEMU hits the below assert
> 
> qemu-system-ppc64: used ring relocated for ring 2
> qemu-system-ppc64: qemu/hw/virtio/vhost.c:649: vhost_commit: Assertion `r >= 
> 0' failed.
> 
> in the following scenario:
> 
> 1. Boot guest with vhost=on
>   -netdev tap,id=mynet0,script=qemu-ifup,downscript=qemu-ifdown,vhost=on 
> -device virtio-net-pci,netdev=mynet0
> 2. Hot add a DIMM device 
> 3. Reboot
>    When the guest reboots, we can see
>    vhost_virtqueue_start:vq->used_phys getting assigned an address that
>    falls in the hotplugged memory range.
> 4. Remove the DIMM device
>    Guest refuses the removal as the hotplugged memory is under use.
> 5. Reboot

>    QEMU forces the removal of the DIMM device during reset and that's
>    when we hit the above assert.
I don't recall implementing forced removal om DIMM,
could you point out to the related code, pls?

> Any pointers on why we are hitting this assert ? Shouldn't vhost be
> done with using the hotplugged memory when we hit reset ?

From another point of view,
DIMM shouldn't be removed unless guest explicitly ejects it
(at least that should be so in x86 case).

> 
> Regards,
> Bharata.
> 
>