Re: [RFC PATCH v2 0/5] virtio: early detect 'modern' virtio

[Michael S. Tsirkin]

On Fri, Nov 12, 2021 at 03:57:44PM +0100, Halil Pasic wrote:
> This is an early RFC for a transport specific early detecton of
> modern virtio, which is most relevant for transitional devices on big
> endian platforms, when drivers access the config space before
> FEATURES_OK is set.
> 
> The most important part that is missing here is fixing all the problems
> that arise in the situation described in the previous paragraph, when
> the config is managed by a vhost device (and thus outside QEMU. This
> series tackles this problem only for virtio_net+vhost as an example. If
> this approach is deemed good, we need to do something very similar for
> every single affected device.
> 
> This series was only lightly tested. The vhost stuff is entirely
> untested, unfortunately I don't have a working setup where this
> handling would be needed (because the config space is handled in the
> device). DPDK is not supported on s390x so at the moment I can't test
> DPDK based setups. 

So this looks sane to me. Cornelia requested some name tweaks and we
need to add vhost-user things and more devices, but otherwise we are
good.

> v1 -> v2:
> 
> * add callback
> * tweak feature manipulation
> * add generic handling for vhost that needs to be called by devices
> * add handling for virtio
> 
> Halil Pasic (5):
>   virtio: introduce virtio_force_modern()
>   virtio-ccw: use virtio_force_modern()
>   virtio-pci: use virtio_force_modern()
>   vhost: push features to backend on force_modern
>   virtio-net: handle force_modern for vhost
> 
>  hw/net/virtio-net.c        | 20 ++++++++++++++++++++
>  hw/s390x/virtio-ccw.c      |  3 +++
>  hw/virtio/vhost.c          | 17 +++++++++++++++++
>  hw/virtio/virtio-pci.c     |  1 +
>  hw/virtio/virtio.c         | 13 +++++++++++++
>  include/hw/virtio/vhost.h  |  2 ++
>  include/hw/virtio/virtio.h |  2 ++
>  7 files changed, 58 insertions(+)
> 
> 
> base-commit: 2c3e83f92d93fbab071b8a96b8ab769b01902475
> -- 
> 2.25.1