Re: [RFC v2 00/13] Dinamycally switch to vhost shadow virtqueues at vdpa net migration

[Si-Wei Liu]

On 1/12/2023 9:24 AM, Eugenio Pérez wrote:
> It's possible to migrate vdpa net devices if they are shadowed from the
>
> start.  But to always shadow the dataplane is effectively break its host
>
> passthrough, so its not convenient in vDPA scenarios.
>
>
>
> This series enables dynamically switching to shadow mode only at
>
> migration time.  This allow full data virtqueues passthrough all the
>
> time qemu is not migrating.
>
>
>
> Successfully tested with vdpa_sim_net (but it needs some patches, I
>
> will send them soon) and qemu emulated device with vp_vdpa with
>
> some restrictions:
>
> * No CVQ.
>
> * VIRTIO_RING_F_STATE patches.
What are these patches (I'm not sure I follow VIRTIO_RING_F_STATE, is it 
a new feature that other vdpa driver would need for live migration)?

-Siwei

> * Expose _F_SUSPEND, but ignore it and suspend on ring state fetch like
>
>    DPDK.
>
>
>
> Comments are welcome, especially in the patcheswith RFC in the message.
>
>
>
> v2:
>
> - Use a migration listener instead of a memory listener to know when
>
>    the migration starts.
>
> - Add stuff not picked with ASID patches, like enable rings after
>
>    driver_ok
>
> - Add rewinding on the migration src, not in dst
>
> - v1 at https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg01664.html
>
>
>
> Eugenio Pérez (13):
>
>    vdpa: fix VHOST_BACKEND_F_IOTLB_ASID flag check
>
>    vdpa net: move iova tree creation from init to start
>
>    vdpa: copy cvq shadow_data from data vqs, not from x-svq
>
>    vdpa: rewind at get_base, not set_base
>
>    vdpa net: add migration blocker if cannot migrate cvq
>
>    vhost: delay set_vring_ready after DRIVER_OK
>
>    vdpa: delay set_vring_ready after DRIVER_OK
>
>    vdpa: Negotiate _F_SUSPEND feature
>
>    vdpa: add feature_log parameter to vhost_vdpa
>
>    vdpa net: allow VHOST_F_LOG_ALL
>
>    vdpa: add vdpa net migration state notifier
>
>    vdpa: preemptive kick at enable
>
>    vdpa: Conditionally expose _F_LOG in vhost_net devices
>
>
>
>   include/hw/virtio/vhost-backend.h |   4 +
>
>   include/hw/virtio/vhost-vdpa.h    |   1 +
>
>   hw/net/vhost_net.c                |  25 ++-
>
>   hw/virtio/vhost-vdpa.c            |  64 +++++---
>
>   hw/virtio/vhost.c                 |   3 +
>
>   net/vhost-vdpa.c                  | 247 +++++++++++++++++++++++++-----
>
>   6 files changed, 278 insertions(+), 66 deletions(-)