linux-kernel - Re: [PATCH V1] vdpa: suspend and resume require DRIVER

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Date: Tue, 13 Feb 2024 09:08:21 +0100
From: Eugenio Perez Martin <eperezma@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Steve Sistare <steven.sistare@...cle.com>, 
	virtualization <virtualization@...ts.linux-foundation.org>, 
	linux-kernel <linux-kernel@...r.kernel.org>, Jason Wang <jasowang@...hat.com>, 
	Si-Wei Liu <si-wei.liu@...cle.com>, Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH V1] vdpa: suspend and resume require DRIVER_OK

On Tue, Feb 13, 2024 at 8:49 AM Eugenio Perez Martin
<eperezma@...hat.com> wrote:
>
> On Mon, Feb 12, 2024 at 9:20 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Fri, Feb 09, 2024 at 02:29:59PM -0800, Steve Sistare wrote:
> > > Calling suspend or resume requires VIRTIO_CONFIG_S_DRIVER_OK, for all
> > > vdpa devices.
> > >
> > > Suggested-by: Eugenio Perez Martin <eperezma@...hat.com>"
> > > Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
> >
> > I don't think failing suspend or resume makes sense though -
> > e.g. practically failing suspend will just prevent sleeping I think -
> > why should guest not having driver loaded prevent
> > system suspend?
> >
>
> In the QEMU case the vhost device has not started, so QEMU should
> allow the system suspension.
>
> I haven't tested the QEMU behavior on suspend (not poweroff) with the
> guest driver loaded, but I think QEMU should indeed block the
> suspension, as there is no way to recover the device after that
> without the guest cooperation?
>
> > there's also state such as features set which does need to be
> > preserved.
> >
>
> That's true if the device does not support resuming. Well, in the
> particular case of features, maybe we need to keep it, as userspace
> could call VHOST_GET_FEATURES. But maybe we can clean some things,
> right.
>
> > I think the thing to do is to skip invoking suspend/resume callback, and in
> > fact checking suspend/resume altogether.
> >
>
> I don't follow this. What should be done in this cases by QEMU?
> 1) The device does not support suspend
> 2) The device support suspend but not resume
>
> In my opinion 1) should be forbidden, as we don't support to resume
> the device properly, and 2) can be allowed by fetching all the state.
>

Ok I missed the whole other thread, everything is clear now.

Thanks!

> Thanks!
>
> > > ---
> > >  drivers/vhost/vdpa.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > > index bc4a51e4638b..ce1882acfc3b 100644
> > > --- a/drivers/vhost/vdpa.c
> > > +++ b/drivers/vhost/vdpa.c
> > > @@ -598,6 +598,9 @@ static long vhost_vdpa_suspend(struct vhost_vdpa *v)
> > >       if (!ops->suspend)
> > >               return -EOPNOTSUPP;
> > >
> > > +     if (!(ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
> > > +             return -EINVAL;
> > > +
> > >       ret = ops->suspend(vdpa);
> > >       if (!ret)
> > >               v->suspended = true;
> > > @@ -618,6 +621,9 @@ static long vhost_vdpa_resume(struct vhost_vdpa *v)
> > >       if (!ops->resume)
> > >               return -EOPNOTSUPP;
> > >
> > > +     if (!(ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
> > > +             return -EINVAL;
> > > +
> > >       ret = ops->resume(vdpa);
> > >       if (!ret)
> > >               v->suspended = false;
> > > --
> > > 2.39.3
> >
> >