Re: [Qemu-devel] Re: [PATCH v4 0/4] virtio: Use ioeventfd for virtqueue notify

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 17, 2010 at 08:38:25PM +0000, Stefan Hajnoczi wrote:
> On Wed, Nov 17, 2010 at 6:01 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Wed, Nov 17, 2010 at 04:19:25PM +0000, Stefan Hajnoczi wrote:
> >> The v4 version includes:
> >>  * Simpler start/stop ioeventfd mechanism using bool ioeventfd_started state
> >>  * Support for migration
> >>  * Handle deassign race condition to avoid dropping a virtqueue kick
> >>  * Add missing kvm_enabled() check to kvm_has_many_ioeventfds()
> >>  * Documentation updates for qdev -device with ioeventfd=on|off
> >
> > Anthony, could you pls remind me what did you say
> > about need to stop these threads on migration vmstop?
> > Or am I confusing this with something else?
> 
> Two points about the VM change state:
> 1. It is used to bring up virtio-ioeventfd on the destination host
> after migration.
> 2. It handles the race condition where a virtqueue kick is dropped
> because we deassign the ioeventfd on the source host.
> 
> So I've implemented the VM change state to get correct migration behavior.
> 
> The discussion you had with Anthony was more about events happening
> while the VM is paused and how that could interfere with guest state
> for migration IIRC.
> 
> Stefan

Exactly. Could your patches cause a situation where block virtio ring
is used after migration stopped a VM?

-- 
MST