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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

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@xxxxxxxxxx
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > >
> > >  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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