netdev - Re: [PATCH v7 0/4] Implement vdpasim suspend operation

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Date:   Wed, 10 Aug 2022 15:19:56 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Eugenio Pérez <eperezma@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        dinang@...inx.com, martinpo@...inx.com,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        Piotr.Uminski@...el.com, gautam.dawar@....com,
        ecree.xilinx@...il.com, martinh@...inx.com,
        Stefano Garzarella <sgarzare@...hat.com>, pabloc@...inx.com,
        habetsm.xilinx@...il.com, lvivier@...hat.com,
        Zhu Lingshan <lingshan.zhu@...el.com>, tanuj.kamde@....com,
        Longpeng <longpeng2@...wei.com>, lulu@...hat.com,
        hanand@...inx.com, Parav Pandit <parav@...dia.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        Eli Cohen <elic@...dia.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Zhang Min <zhang.min9@....com.cn>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH v7 0/4] Implement vdpasim suspend operation

On Wed, Aug 10, 2022 at 07:15:08PM +0200, Eugenio Pérez wrote:
> Implement suspend operation for vdpa_sim devices, so vhost-vdpa will offer
> that backend feature and userspace can effectively suspend the device.
> 
> This is a must before getting 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 a successful return of ioctl the device must not process more virtqueue
> descriptors. The device can answer to read or writes of config fields as if it
> were not suspended. In particular, writing to "queue_enable" with a value of 1
> will not make the device start processing virtqueue buffers.
> 
> In the future, we will provide features similar to
> VHOST_USER_GET_INFLIGHT_FD so the device can save pending operations.
> 
> Applied on top of [1] branch after removing the old commits.

Except, I can't really do this without invaliding all testing.
Can't you post an incremental patch?

> Comments are welcome.
> 
> v7:
> * Remove ioctl leftover argument and update doc accordingly.

> v6:
> * Remove the resume operation, making the ioctl simpler. We can always add
>   another ioctl for VM_STOP/VM_RESUME operation later.
> * s/stop/suspend/ to differentiate more from reset.
> * Clarify scope of the suspend operation.
> 
> v5:
> * s/not stop/resume/ in doc.
> 
> 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.
> 
> [1] git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git
> 
> Eugenio Pérez (4):
>   vdpa: Add suspend operation
>   vhost-vdpa: introduce SUSPEND backend feature bit
>   vhost-vdpa: uAPI to suspend the device
>   vdpa_sim: Implement suspend vdpa op
> 
>  drivers/vdpa/vdpa_sim/vdpa_sim.c     | 14 +++++++++++
>  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                 | 35 +++++++++++++++++++++++++++-
>  include/linux/vdpa.h                 |  4 ++++
>  include/uapi/linux/vhost.h           |  9 +++++++
>  include/uapi/linux/vhost_types.h     |  2 ++
>  8 files changed, 70 insertions(+), 1 deletion(-)
> 
> -- 
> 2.31.1
>