linux-kernel - Re: [Xen-devel] [PATCH 2/3] xen/ring: Add a new macro to detect whether there is an overflow in requests and response.

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Message-ID: <20130125182902.GB32372@phenom.dumpdata.com>
Date:	Fri, 25 Jan 2013 13:29:02 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Roger Pau Monné <roger.pau@...rix.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/3] xen/ring: Add a new macro to detect
 whether there is an overflow in requests and response.

On Fri, Jan 25, 2013 at 06:45:29PM +0100, Roger Pau Monné wrote:
> On 25/01/13 18:32, Konrad Rzeszutek Wilk wrote:
> > We want to be able to exit if the difference between the request
> > produced (what the frontend tells us) and the requests consumed
> > (what we have so far processed) is greater than the ring size.
> > 
> > If so, we should terminate the loop as the request produced
> > is not trusted and it means it is bogus.
> > 
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > ---
> >  include/xen/interface/io/ring.h | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
> > index 75271b9..1114dde 100644
> > --- a/include/xen/interface/io/ring.h
> > +++ b/include/xen/interface/io/ring.h
> > @@ -188,6 +188,12 @@ struct __name##_back_ring {						\
> >  #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)				\
> >      (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
> >  
> > +/* Loop termination condition: Is the difference between request produced
> > + * and request consumed greater than the ring size. If so, terminate the
> > + * loop. */
> > +#define RING_REQUEST_PROD_OVERFLOW(_r, _cons, _prod)                     \
> > +    (((_prod) - (_prod)) > RING_SIZE(_r))
> 
> Shouldn't the second _prod be _cons?

Yes :-) Was just testing everybody :-)

> 
> > +
> >  #define RING_PUSH_REQUESTS(_r) do {					\
> >      wmb(); /* back sees requests /before/ updated producer index */	\
> >      (_r)->sring->req_prod = (_r)->req_prod_pvt;				\
> > 
> 
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