linux-kernel - Re: [PATCH vhost v4 06/15] vdpa: Track device suspended state

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Date: Fri, 22 Dec 2023 11:22:40 +0000
From: Dragos Tatulea <dtatulea@...dia.com>
To: "jasowang@...hat.com" <jasowang@...hat.com>
CC: "xuanzhuo@...ux.alibaba.com" <xuanzhuo@...ux.alibaba.com>, Parav Pandit
	<parav@...dia.com>, Gal Pressman <gal@...dia.com>, "eperezma@...hat.com"
	<eperezma@...hat.com>, "virtualization@...ts.linux-foundation.org"
	<virtualization@...ts.linux-foundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "si-wei.liu@...cle.com"
	<si-wei.liu@...cle.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>, Saeed Mahameed <saeedm@...dia.com>,
	"leon@...nel.org" <leon@...nel.org>
Subject: Re: [PATCH vhost v4 06/15] vdpa: Track device suspended state

On Wed, 2023-12-20 at 13:55 +0100, Dragos Tatulea wrote:
> On Wed, 2023-12-20 at 11:46 +0800, Jason Wang wrote:
> > On Wed, Dec 20, 2023 at 2:09 AM Dragos Tatulea <dtatulea@...dia.com> wrote:
> > > 
> > > Set vdpa device suspended state on successful suspend. Clear it on
> > > successful resume and reset.
> > > 
> > > The state will be locked by the vhost_vdpa mutex. The mutex is taken
> > > during suspend, resume and reset in vhost_vdpa_unlocked_ioctl. The
> > > exception is vhost_vdpa_open which does a device reset but that should
> > > be safe because it can only happen before the other ops.
> > > 
> > > Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> > > Suggested-by: Eugenio Pérez <eperezma@...hat.com>
> > > ---
> > >  drivers/vhost/vdpa.c | 17 +++++++++++++++--
> > >  1 file changed, 15 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > > index b4e8ddf86485..00b4fa8e89f2 100644
> > > --- a/drivers/vhost/vdpa.c
> > > +++ b/drivers/vhost/vdpa.c
> > > @@ -59,6 +59,7 @@ struct vhost_vdpa {
> > >         int in_batch;
> > >         struct vdpa_iova_range range;
> > >         u32 batch_asid;
> > > +       bool suspended;
> > 
> > Any reason why we don't do it in the core vDPA device but here?
> > 
> Not really. I wanted to be safe and not expose it in a header due to locking.
> 
A few clearer answers for why the state is not added in struct vdpa_device:
- All the suspend infrastructure is currently only for vhost.
- If the state would be moved to struct vdpa_device then the cf_lock would have
to be used. This adds more complexity to the code.

Thanks,
Dragos