netdev - Re: [PATCH v8 0/3] Implement vdpasim suspend operation

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Date:   Thu, 11 Aug 2022 16:25:47 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     virtualization <virtualization@...ts.linux-foundation.org>,
        Jason Wang <jasowang@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, ecree.xilinx@...il.com,
        "Dawar, Gautam" <gautam.dawar@....com>,
        Zhang Min <zhang.min9@....com.cn>,
        Pablo Cascon Katchadourian <pabloc@...inx.com>,
        "Uminski, Piotr" <Piotr.Uminski@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "Kamde, Tanuj" <tanuj.kamde@....com>,
        Zhu Lingshan <lingshan.zhu@...el.com>,
        Martin Petrus Hubertus Habets <martinh@...inx.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Laurent Vivier <lvivier@...hat.com>,
        Martin Porter <martinpo@...inx.com>,
        Harpreet Singh Anand <hanand@...inx.com>,
        Eli Cohen <elic@...dia.com>, Cindy Lu <lulu@...hat.com>,
        habetsm.xilinx@...il.com, Parav Pandit <parav@...dia.com>,
        Longpeng <longpeng2@...wei.com>,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Dinan Gunawardena <dinang@...inx.com>,
        Xie Yongji <xieyongji@...edance.com>
Subject: Re: [PATCH v8 0/3] Implement vdpasim suspend operation

On Thu, Aug 11, 2022 at 3:58 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Aug 11, 2022 at 03:53:50PM +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 vhost branch.
> >
> > Comments are welcome.
> >
> > v8:
> > * v7 but incremental from vhost instead of isolated.
>
> Now I'm lost. incremental to what? Does the vhost branch now
> have the correct bits?
>

This patch is intended to be applied on top of the current vhost
branch. In particular, on the top of commit
6a9720576cd00d30722c5f755bd17d4cfa9df636.

It basically deletes the code, the doc, and the unused ioctl argument.

Did I misunderstand what you meant with "incremental" in previous mail?

> > 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 (3):
> >   vdpa: delete unreachable branch on vdpasim_suspend
> >   vdpa: Remove wrong doc of VHOST_VDPA_SUSPEND ioctl
> >   vhost: Remove invalid parameter of VHOST_VDPA_SUSPEND ioctl
> >
> >  drivers/vdpa/vdpa_sim/vdpa_sim.c |  7 -------
> >  include/linux/vdpa.h             |  2 +-
> >  include/uapi/linux/vhost.h       | 17 ++++++-----------
> >  3 files changed, 7 insertions(+), 19 deletions(-)
> >
> > --
> > 2.31.1
> >
>