Re: [Xen-devel] [PATCH v3] io/ring.h: new macro to detect whether there are too many requests on the ring

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 11/06/2013 09:23, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Backends may need to protect themselves against an insane number of
> produced requests stored by a frontend, in case they iterate over
> requests until reaching the req_prod value. There can't be more
> requests on the ring than the difference between produced requests
> and produced (but possibly not yet published) responses.
> 
> This is a more strict alternative to a patch previously posted by
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/include/public/io/ring.h
> +++ b/xen/include/public/io/ring.h
> @@ -234,6 +234,10 @@ typedef struct __name##_back_ring __name
>  #define RING_REQUEST_CONS_OVERFLOW(_r, _cons)                           \
>      (((_cons) - (_r)->rsp_prod_pvt) >= RING_SIZE(_r))
>  
> +/* Ill-behaved frontend determination: Can there be this many requests? */
> +#define RING_REQUEST_PROD_OVERFLOW(_r, _prod)                           \
> +    (((_prod) - (_r)->rsp_prod_pvt) > RING_SIZE(_r))
> +
>  #define RING_PUSH_REQUESTS(_r) do {                                     \
>      xen_wmb(); /* back sees requests /before/ updated producer index */ \
>      (_r)->sring->req_prod = (_r)->req_prod_pvt;                         \
> 
> 
> 
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