[PATCH 4.15 088/122] s390/qeth: fix underestimated count of buffer elements

[Greg Kroah-Hartman]

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

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

From: Ursula Braun <ubraun@xxxxxxxxxxxxxxxxxx>


[ 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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Julian Wiedmann <jwi@xxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 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
@@ -836,7 +836,7 @@ 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)