linux-kernel - Re: [Xen-devel] [PATCH 2/4] xen/hvc: Fix error cases around HVM_PARAM_CONSOLE

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Message-ID: <20120524181859.GK24934@phenom.dumpdata.com>
Date:	Thu, 24 May 2012 14:18:59 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/4] xen/hvc: Fix error cases around
 HVM_PARAM_CONSOLE_PFN

On Thu, May 24, 2012 at 01:31:10PM -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, May 24, 2012 at 11:47:12AM +0100, Stefano Stabellini wrote:
> > On Wed, 23 May 2012, Konrad Rzeszutek Wilk wrote:
> > > We weren't resetting the parameter to be passed in to a
> > > known default. Nor were we checking the return value of
> > > hvm_get_parameter.
> > > 
> > > CC: stable@...nel.org
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > >
> > >  drivers/tty/hvc/hvc_xen.c |    3 ++-
> > >  1 files changed, 2 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
> > > index afc7fc2..3277f0e 100644
> > > --- a/drivers/tty/hvc/hvc_xen.c
> > > +++ b/drivers/tty/hvc/hvc_xen.c
> > > @@ -219,7 +219,8 @@ static int xen_hvm_console_init(void)
> > >  	if (r < 0)
> > >  		goto err;
> > >  	info->evtchn = v;
> > > -	hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &v);
> > > +	v = 0;
> > > +	r = hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &v);
> > >  	if (r < 0)
> > >  		goto err;
> > >  	mfn = v;
> > 
> > Is 0 the right default here?
> > Maybe something invalid like (~0UL) would be better?
> 
> Perhaps both? The zero is the default non-initialized value. But
> -0UL is also a good check value.

Somehow I misread your comment as checking the return value, not the
default value.

I think zero is the right choice as that is the default non-initialized
value.
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