linux-kernel - [PATCH 1/2] xen/io/ring.h: new macro to detect whether there are too many requests on the ring

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Message-Id: <1371498454-2116-2-git-send-email-konrad.wilk@oracle.com>
Date:	Mon, 17 Jun 2013 15:47:33 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	jbeulich@...e.com, xen-devel@...ts.xensource.com,
	linux-kernel@...r.kernel.org
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: [PATCH 1/2] xen/io/ring.h: new macro to detect whether there are too many requests on the ring

From: Jan Beulich <jbeulich@...e.com>

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@...cle.com>.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
---
 include/xen/interface/io/ring.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
index 75271b9..7d28aff 100644
--- a/include/xen/interface/io/ring.h
+++ b/include/xen/interface/io/ring.h
@@ -188,6 +188,11 @@ struct __name##_back_ring {						\
 #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 {					\
     wmb(); /* back sees requests /before/ updated producer index */	\
     (_r)->sring->req_prod = (_r)->req_prod_pvt;				\
-- 
1.8.1.4

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