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

Roger Pau Monné
2013-01-25T17:55:25Z

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

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