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

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Message-ID: <CACGkMEuC29vaBPi7jDED3DzxPuZZx2hrUmtEUv4UWSdTM5AcFQ@mail.gmail.com>
Date:   Tue, 31 May 2022 14:44:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Parav Pandit <parav@...dia.com>,
        Eugenio Pérez <eperezma@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "martinh@...inx.com" <martinh@...inx.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "martinpo@...inx.com" <martinpo@...inx.com>,
        "lvivier@...hat.com" <lvivier@...hat.com>,
        "pabloc@...inx.com" <pabloc@...inx.com>,
        Eli Cohen <elic@...dia.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Zhang Min <zhang.min9@....com.cn>,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        Zhu Lingshan <lingshan.zhu@...el.com>,
        "Piotr.Uminski@...el.com" <Piotr.Uminski@...el.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        "ecree.xilinx@...il.com" <ecree.xilinx@...il.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>,
        "habetsm.xilinx@...il.com" <habetsm.xilinx@...il.com>,
        "tanuj.kamde@....com" <tanuj.kamde@....com>,
        "hanand@...inx.com" <hanand@...inx.com>,
        "dinang@...inx.com" <dinang@...inx.com>,
        Longpeng <longpeng2@...wei.com>
Subject: Re: [PATCH v4 0/4] Implement vdpasim stop operation

On Tue, May 31, 2022 at 1:40 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Mon, May 30, 2022 at 11:39:21AM +0800, Jason Wang wrote:
> > On Fri, May 27, 2022 at 6:56 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> > >
> > > On Thu, May 26, 2022 at 12:54:32PM +0000, Parav Pandit wrote:
> > > >
> > > >
> > > > > From: Eugenio Pérez <eperezma@...hat.com>
> > > > > Sent: Thursday, May 26, 2022 8:44 AM
> > > >
> > > > > 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.
> > > > >
> > > > >
> > > > >
> > > > > 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).
> > > >
> > > > Just to be clear, we are adding vdpa level new ioctl() that doesn’t map to any mechanism in the virtio spec.
> > > >
> > > > Why can't we use this ioctl() to indicate driver to start/stop the device instead of driving it through the driver_ok?
> > > > This is in the context of other discussion we had in the LM series.
> > >
> > > If there's something in the spec that does this then let's use that.
> >
> > Actually, we try to propose a independent feature here:
> >
> > https://lists.oasis-open.org/archives/virtio-dev/202111/msg00020.html
> >
> > Does it make sense to you?
> >
> > Thanks
>
> But I thought the LM patches are trying to replace all that?

I'm not sure, and actually I think they are orthogonal. We need a new
state and the command to set the state could be transport specific or
a virtqueue.

As far as I know, most of the vendors have implemented this semantic.

Thanks

>
>
> > > Unfortunately the LM series seems to be stuck on moving
> > > bits around with the admin virtqueue ...
> > >
> > > --
> > > MST
> > >
>