Re: [PATCH v4 0/4] Implement vdpasim stop operation

[Jason Wang]

在 2022/5/26 20:43, Eugenio Pérez 写道:
> Implement stop operation for vdpa_sim devices, so vhost-vdpa will offer
> that backend feature and userspace can effectively stop the device.
>
> This is a must before get virtqueue indexes (base) for live migration,
> since the device could modify them after userland gets them. There are
> individual ways to perform that action for some devices
> (VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...) but there was no
> way to perform it for any vhost device (and, in particular, vhost-vdpa).
>
> After the return of ioctl with stop != 0, the device MUST finish any
> pending operations like in flight requests. It must also preserve all
> the necessary state (the virtqueue vring base plus the possible device
> specific states) that is required for restoring in the future. The
> device must not change its configuration after that point.


I think we probably need more accurate definition on the state as Parav 
suggested.

Besides this, we should also clarify when stop is allowed. E.g should we 
allow setting stop without DRIVER_OK?

Thanks


> After the return of ioctl with stop == 0, the device can continue
> processing buffers as long as typical conditions are met (vq is enabled,
> DRIVER_OK status bit is enabled, etc).
>
> In the future, we will provide features similar to VHOST_USER_GET_INFLIGHT_FD
> so the device can save pending operations.
>
> Comments are welcome.
>
> v4:
> * Replace VHOST_STOP to VHOST_VDPA_STOP in vhost ioctl switch case too.
>
> v3:
> * s/VHOST_STOP/VHOST_VDPA_STOP/
> * Add documentation and requirements of the ioctl above its definition.
>
> v2:
> * Replace raw _F_STOP with BIT_ULL(_F_STOP).
> * Fix obtaining of stop ioctl arg (it was not obtained but written).
> * Add stop to vdpa_sim_blk.
>
> Eugenio Pérez (4):
>    vdpa: Add stop operation
>    vhost-vdpa: introduce STOP backend feature bit
>    vhost-vdpa: uAPI to stop the device
>    vdpa_sim: Implement stop vdpa op
>
>   drivers/vdpa/vdpa_sim/vdpa_sim.c     | 21 +++++++++++++++++
>   drivers/vdpa/vdpa_sim/vdpa_sim.h     |  1 +
>   drivers/vdpa/vdpa_sim/vdpa_sim_blk.c |  3 +++
>   drivers/vdpa/vdpa_sim/vdpa_sim_net.c |  3 +++
>   drivers/vhost/vdpa.c                 | 34 +++++++++++++++++++++++++++-
>   include/linux/vdpa.h                 |  6 +++++
>   include/uapi/linux/vhost.h           | 14 ++++++++++++
>   include/uapi/linux/vhost_types.h     |  2 ++
>   8 files changed, 83 insertions(+), 1 deletion(-)