linux-kernel - Re: [PATCH v3 04/16] virtio/console: verify device has config space

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Date:	Tue, 20 Jan 2015 13:09:55 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	cornelia.huck@...ibm.com, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 04/16] virtio/console: verify device has config space

On Tue, Jan 20, 2015 at 04:10:40PM +0530, Amit Shah wrote:
> On (Wed) 14 Jan 2015 [19:27:35], Michael S. Tsirkin wrote:
> > Some devices might not implement config space access
> > (e.g. remoteproc used not to - before 3.9).
> > virtio/console needs config space access so make it
> > fail gracefully if not there.
> 
> Do we know any such devices?  Wondering what prompted this patch.  If
> it's just theoretical, I'd rather let it be like this, and pull this
> in when there's a device that doesn't have config space.

Yes, with virtio 1.0 config space can be in a separate BAR now.  If
that's not enabled by BIOS (e.g. out of space), we won't have config
space.

> Also, just the console functionality (i.e. F_MULTIPORT is unset) is
> available w/o config space access.

Supporting this by gracefully disabling F_MULTIPORT
would require getting this info from driver before
features are finalized.
Alternatively, check F_MULTIPORT and only fail if set?
Let me know, I'll cook up a patch.

> In fact, getting this patch in
> would mean remoteproc wouldn't even run in its pre-config days...

It seems to have get callback unconditionally now - or did I miss
something?


> > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > index de03df9..26afb56 100644
> > --- a/drivers/char/virtio_console.c
> > +++ b/drivers/char/virtio_console.c
> > @@ -1986,6 +1986,12 @@ static int virtcons_probe(struct virtio_device *vdev)
> >  	bool multiport;
> >  	bool early = early_put_chars != NULL;
> >  
> > +	if (!vdev->config->get) {
> > +		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> > +			__func__);
> > +		return -EINVAL;
> > +	}
> > +
> 
> 
> 		Amit
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