From mboxrd@z Thu Jan  1 00:00:00 1970
From: Halil Pasic <pasic@linux.ibm.com>
Subject: Re: [PATCH 06/10] s390/cio: add basic protected virtualization support
Date: Wed, 8 May 2019 23:08:09 +0200
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To: Sebastian Ott <sebott@linux.ibm.com>
Cc: Farhan Ali <alifm@linux.ibm.com>, linux-s390@vger.kernel.org, Thomas Huth <thuth@redhat.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, kvm@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>, Cornelia Huck <cohuck@redhat.com>, Eric Farman <farman@linux.ibm.com>, virtualization@lists.linux-foundation.org, Christoph Hellwig <hch@infradead.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Viktor Mihajlovski <mihajlov@linux.ibm.com>, Janosch Frank <frankja@linux.ibm.com>
List-Id: virtualization@lists.linuxfoundation.org

On Wed, 8 May 2019 15:46:42 +0200 (CEST)
Sebastian Ott <sebott@linux.ibm.com> wrote:

> 
> On Fri, 26 Apr 2019, Halil Pasic wrote:
> >  static struct ccw_device * io_subchannel_allocate_dev(struct subchannel *sch)
> >  {
> [..]
> > +	cdev->private = kzalloc(sizeof(struct ccw_device_private),
> > +				GFP_KERNEL | GFP_DMA);
> 
> Do we still need GFP_DMA here (since we now have cdev->private->dma_area)?
> 

We probably do not. I kept it GFP_DMA to keep changes to the
minimum. Should changing this in your opinion be a part of this patch?

> > @@ -1062,6 +1082,14 @@ static int io_subchannel_probe(struct subchannel *sch)
> >  	if (!io_priv)
> >  		goto out_schedule;
> >  
> > +	io_priv->dma_area = dma_alloc_coherent(&sch->dev,
> > +				sizeof(*io_priv->dma_area),
> > +				&io_priv->dma_area_dma, GFP_KERNEL);
> 
> This needs GFP_DMA.

Christoph already answered this one. Thanks Christoph!

> You use a genpool for ccw_private->dma and not for iopriv->dma - looks
> kinda inconsistent.
> 

Please have a look at patch #9. A virtio-ccw device uses the genpool of
it's ccw device (the pool from which ccw_private->dma is allicated) for
the ccw stuff it needs to do. AFAICT for a subchannel device and its API
all the DMA memory we need is iopriv->dma. So my thought was
constructing a genpool for that would be an overkill.

Are you comfortable with this answer, or should we change something?

Regards,
Halil