linux-kernel - [PATCH 4.9 49/65] s390/qeth: fix underestimated count of buffer elements

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Date:   Fri,  9 Mar 2018 16:18:49 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ursula Braun <ubraun@...ux.vnet.ibm.com>,
        Julian Wiedmann <jwi@...ux.vnet.ibm.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 49/65] s390/qeth: fix underestimated count of buffer elements

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ursula Braun <ubraun@...ux.vnet.ibm.com>

[ Upstream commit 89271c65edd599207dd982007900506283c90ae3 ]

For a memory range/skb where the last byte falls onto a page boundary
(ie. 'end' is of the form xxx...xxx001), the PFN_UP() part of the
calculation currently doesn't round up to the next PFN due to an
off-by-one error.
Thus qeth believes that the skb occupies one page less than it
actually does, and may select a IO buffer that doesn't have enough spare
buffer elements to fit all of the skb's data.
HW detects this as a malformed buffer descriptor, and raises an
exception which then triggers device recovery.

Fixes: 2863c61334aa ("qeth: refactor calculation of SBALE count")
Signed-off-by: Ursula Braun <ubraun@...ux.vnet.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@...ux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/s390/net/qeth_core.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -849,7 +849,7 @@ struct qeth_trap_id {
  */
 static inline int qeth_get_elements_for_range(addr_t start, addr_t end)
 {
-	return PFN_UP(end - 1) - PFN_DOWN(start);
+	return PFN_UP(end) - PFN_DOWN(start);
 }

 static inline int qeth_get_micros(void)