QEMU v8.0 is able to switch dynamically between vhost-vdpa passthrough
and SVQ mode as long as the net device does not have CVQ.  The net device
state followed (and migrated) by CVQ requires special care.

A pre-requisite to add CVQ to that framework is to determine if devices with
CVQ are migratable or not at initialization time.  The solution to it is to
always shadow only CVQ, and vq groups and ASID are used for that.

However, current qemu version only checks ASID at device start (as "driver set
DRIVER_OK status bit"), not at device initialization.  A check at
initialization time is required.  Otherwise, the guest would be able to set
and remove migration blockers at will [1].

This series is a requisite for migration of vhost-vdpa net devices with CVQ.
However it already makes sense by its own, as it reduces the number of ioctls
at migration time, decreasing the error paths there.

[1] https://lore.kernel.org/qemu-devel/2616f0cd-f9e8-d183-ea78-db1be4825d9c@redhat.com/
---
v3:
* Only record cvq_isolated, true if the device have cvq isolated in both !MQ
* and MQ configurations.
* Drop the cache of cvq group, it can be done on top

v2:
* Take out the reset of the device from vhost_vdpa_cvq_is_isolated
  (reported by Lei Yang).
* Expand patch messages by Stefano G. questions.

Eugenio Pérez (5):
  vdpa: Remove status in reset tracing
  vdpa: add vhost_vdpa_reset_status_fd
  vdpa: add vhost_vdpa_set_dev_features_fd
  vdpa: return errno in vhost_vdpa_get_vring_group error
  vdpa: move CVQ isolation check to net_init_vhost_vdpa

 include/hw/virtio/vhost-vdpa.h |   2 +
 hw/virtio/vhost-vdpa.c         |  78 ++++++++++-----
 net/vhost-vdpa.c               | 171 ++++++++++++++++++++++++++-------
 hw/virtio/trace-events         |   2 +-
 4 files changed, 192 insertions(+), 61 deletions(-)

-- 
2.31.1

QE tested this series with sanity testing on the vdpa_sim device,
everything are works fine and there is no any new regression problems.

Tested-by: Lei Yang <leiyang@redhat.com>



On Tue, May 9, 2023 at 11:44 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> QEMU v8.0 is able to switch dynamically between vhost-vdpa passthrough
> and SVQ mode as long as the net device does not have CVQ.  The net device
> state followed (and migrated) by CVQ requires special care.
>
> A pre-requisite to add CVQ to that framework is to determine if devices with
> CVQ are migratable or not at initialization time.  The solution to it is to
> always shadow only CVQ, and vq groups and ASID are used for that.
>
> However, current qemu version only checks ASID at device start (as "driver set
> DRIVER_OK status bit"), not at device initialization.  A check at
> initialization time is required.  Otherwise, the guest would be able to set
> and remove migration blockers at will [1].
>
> This series is a requisite for migration of vhost-vdpa net devices with CVQ.
> However it already makes sense by its own, as it reduces the number of ioctls
> at migration time, decreasing the error paths there.
>
> [1] https://lore.kernel.org/qemu-devel/2616f0cd-f9e8-d183-ea78-db1be4825d9c@redhat.com/
> ---
> v3:
> * Only record cvq_isolated, true if the device have cvq isolated in both !MQ
> * and MQ configurations.
> * Drop the cache of cvq group, it can be done on top
>
> v2:
> * Take out the reset of the device from vhost_vdpa_cvq_is_isolated
>   (reported by Lei Yang).
> * Expand patch messages by Stefano G. questions.
>
> Eugenio Pérez (5):
>   vdpa: Remove status in reset tracing
>   vdpa: add vhost_vdpa_reset_status_fd
>   vdpa: add vhost_vdpa_set_dev_features_fd
>   vdpa: return errno in vhost_vdpa_get_vring_group error
>   vdpa: move CVQ isolation check to net_init_vhost_vdpa
>
>  include/hw/virtio/vhost-vdpa.h |   2 +
>  hw/virtio/vhost-vdpa.c         |  78 ++++++++++-----
>  net/vhost-vdpa.c               | 171 ++++++++++++++++++++++++++-------
>  hw/virtio/trace-events         |   2 +-
>  4 files changed, 192 insertions(+), 61 deletions(-)
>
> --
> 2.31.1
>
>