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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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@kernel.org
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.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.