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

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Date: Mon, 12 Feb 2024 10:56:44 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Steven Sistare <steven.sistare@...cle.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Jason Wang <jasowang@...hat.com>,
	Si-Wei Liu <si-wei.liu@...cle.com>,
	Eugenio Perez Martin <eperezma@...hat.com>,
	Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH V1] vdpa: suspend and resume require DRIVER_OK

On Mon, Feb 12, 2024 at 09:56:31AM -0500, Steven Sistare wrote:
> On 2/12/2024 3:19 AM, Michael S. Tsirkin 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?
> 
> Got it, my fix is too heavy handed.
> 
> > there's also state such as features set which does need to be
> > preserved.
> > 
> > I think the thing to do is to skip invoking suspend/resume callback
> 
> OK.
> 
> >  and in
> > fact checking suspend/resume altogether.
> 
> Currently ops->suspend, vhost_vdpa_can_suspend(), and VHOST_BACKEND_F_SUSPEND
> are equivalent.  Hence if !ops->suspend, then then the driver does not support
> it, and indeed may break if suspend is used, so system suspend must be blocked,
> AFAICT.  Yielding:

If DRIVER_OK is not set then there's nothing to be done for migration.
So callback not needed.


>     vhost_vdpa_suspend()
>         if (!ops->suspend)
>             return -EOPNOTSUPP;
> 
>         if (!(ops->get_status(vdpa) & VIRTIO_CONFIG_S_DRIVER_OK))
>             return 0;
> 
> - Steve
> 
> >> ---
> >>  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
> >