s390/qeth: fix underestimated count of buffer elements

Web:        https://git.kernel.org/torvalds/c/89271c65edd599207dd982007900506283c90ae3
Commit:     89271c65edd599207dd982007900506283c90ae3
Parent:     0bf7800f1799b5b1fd7d4f024e9ece53ac489011
Refname:    refs/heads/master
Author:     Ursula Braun <[email protected]>
AuthorDate: Fri Feb 9 11:03:49 2018 +0100
Committer:  David S. Miller <[email protected]>
CommitDate: Fri Feb 9 14:30:23 2018 -0500

    s390/qeth: fix underestimated count of buffer elements
    
    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 <[email protected]>
    Signed-off-by: Julian Wiedmann <[email protected]>
    Signed-off-by: David S. Miller <[email protected]>
---
 drivers/s390/net/qeth_core.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
index db42107bf2f5..c33fbc4c2e91 100644
--- a/drivers/s390/net/qeth_core.h
+++ b/drivers/s390/net/qeth_core.h
@@ -846,7 +846,7 @@ 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)
--
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